coursefinal-part1

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Introduction

to

Geographic Information System (GIS)

Dr. Mohamed Nour Eldien


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Table of content Chapter 1:Introduction to GIS

What is GIS Geographic Information System?

MAPS AND MAP ANALYSIS

Chapter 2:Geometric data acquisition techniques

Chapter 3:GIS Data Model: Vector Data model

Chapter 4:GIS Data Model: Raster Data model

Chapter 5: GIS Application Network analysis
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What is GIS?

GIS = Geographic Information System(s)

GIS is a collection of computer hardware, software, and geographic data for

capturing, managing, analyzing, and displaying all forms of geographicallyreferenced information.

Environmental Systems Research Institute (ESRI), 2007


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What is GIS?

GIS = Geographic Information System(s)

GIS is a collection of computer hardware, software, and geographic data for

capturing, managing, analyzing, and displayingall forms of geographicallyreferenced information.

Environmental Systems Research Institute (ESRI), 2007


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Definition of GIS (1)

Geographic Information System:

An organized collection of computer hardware,

software, geographic data, and personneldesigned to efficiently capture, store, update,

manipulate, analyze and display all forms of

geographically referenced information.from Understanding GISThe ARC/INFO Method, ESRI,

1993


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G I S


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Kingston Centre for GIS 7

GIS concepts are not new!

London cholera epidemic 1854

Cholera death

Water pump

Soho

+


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Kingston Centre for GIS 8

Spatial information handling 1854

Cholera death

Water pump

Soho

+


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Chapter1:What is GIS Geographic Information System?A geographic information system (GIS)uses computers and software to control

the fundamental principle of geographythat location is important in peoples lives.

GIS combines layers of information about a place to give you a better

understanding of that place.

What layers of information you combine depends on

your purpose finding the best location for a new store, analyzing environmental

damage, viewing similar crimes in a city to detect a pattern, and so on.

Why is th is layer ing so impor tant?

The power of a GIS over paper maps is your ability

to select the information you need to see according

to what goal you are trying to achieve.

A business person trying to map customers in

a particular city will want to see very different

information than a water engineer who wantsto see the water pipelines

for the same city.

Both may start with a common

mapa street and neighborhood map of the city

but the information they add to that map will differ.

Integrate data in various

formats from many sources

using GIS.


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The Basic Of GIS

The short history of GIS(it goes back to the late 1960's) was founded in attempts in the UK, Canada

and US to automate some of the land-management and census activities of government.

Figuring out how to do that, and how to explain what went wrong when they tried, was the start of the

science of GIS. It was realized that many map-related concepts that seem so simple to us (scale, aboundary), required a lot of effort to teach to a computer.

What is a GIS?

The name says it all, but we have to understand the implications of the words in the name.


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GISand Related Software


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GIS ConceptsThis section covers the two basic GIS concepts you need to know to effectively use any GIS

maps

GIS Concept #1: Features have attributes associated with them.

Imagine a tree. How would you keep track of and communicate information about this tree to

other people who need to know all about it? You might use a database to keep track of whatspecies it is, how old it is, how tall it is, how healthy it is, and any other attributes that are

important. This tree is one recordin a database. We call each category (i.e. tree height) a

field.

Layers representing the real

world

Now imagine a grove of

trees that you need to keep

track of attributes for.

Because we are now dealing

with more than one tree, it

becomes relevant where

each tree is so we know

what information relates to

which tree


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We map the location of each tree and identify which attributes belong to which tree. This is the

foundation of GIS. A GIS tells us wheresome is. Computers are synonymous with GIS, and

using a computer we can have hundreds of fields (different attributes) for millions of records

(trees).

GIS Concept # 2: Information is separated into layers.We can also have other layersof information in our GIS.

Our infor-mation on trees would constitute one layer

of information. We could also have a layer with

rivers and a layer with soil types.

Any information can be represented as a layer

A map represents the landscape in an artificial way.

Vecto r layersrepresent features in one of several ways:

Points: A point is good for representing information

in which it is necessary to show where a feature is,

but its physical shape is not important

(i.e. trees in the old growth tree layer).

Lines: A line is suitable to represent many real world features

(i.e. the rivers in the river layer).

Polygons: Don't be intimidated by the name. It is really just a solid multi-sided shape. When

you see a polygon, remember that everything inside the boundary has the attributes

associated with the record. (i.e. soil types in the soils layer)


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You might hear people talk about co verage, Geodatabase,or shapef i le.All these

terms are other names for layersof information.

With individual layers we can conduct analysis between layers and

only display layers of interest

How GIS deals with layered data?GIS takes the numbers and

words from the rows and

columns in databases and

spreadsheets and puts them

on a map. Placing your data

on a map highlights whereyou have many customers if

Combining attributes and Geometry in GIS

you own a store, or lots of

leaks in your water system if

you run a water company. It allows you to view, understand, question, interpret, and

visualize your data in ways simply not possible in the rows and columns of aspreadsheet. And, with data on a map, you can ask more questions. You can ask

Where?, Why?, and How?, all with the location information on hand.


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Geographic Information Systems

GIS Concept

FOR 220 Aerial Photo Interpretation and Forest Measurements

ESRI 2004

ESRI 2004

Keep spatial data and

their attributes where

you can combine

them and ask

questions.


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2. GIS Functions

DataInput & Management

Spatial

Attribute

Quality Control & Database Management

DataManipulation:Geo-processing

Analysis & Modeling

InformationOutput Maps, charts, tables, reports


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Data Input

Satellite ImageryAir

Photos

Digital

Elevation

ModelTiger/Line

Digitize Scan

TransformationTransformation

GPS


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Output

Maps

Charts

Reports


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Triad of Geography

Where

When What

Where: locations When: time

What: thingsproperties/attributes

Why? How?


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Methods of representing geographic space

Raster

Vector


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Geometry, topology and

attributes Geometry: coordinates Topology: adjacency relations of objects

Attributes: properties, values

Example: Country map of South America

Geometry: coordinates of the borders

Topology: which countries border which Attributes: names ofcountries, population, etc.


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3. GIS Components

Organized collection of

Hardware

Network

Software

Data

People

Procedures

People

Software

Data

Procedures

Hardware

Network


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2005 John Wiley & Sons, Ltd

Scanner


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Vector Over Raster


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Projection Methods

Plane, cylinder and cone projections can be:

Simple - tangent to the globe at a point, parallel, or meridian, or

Secant- passing through the earth (multiple standard lines.

The deformation increases with distance from the tangent point or standard lines.

Map DigitizingMethod of converting information from

one format to another using a trace

methodology. Traditionally, digitizing

has meant the creation of a spatial

dataset from a hardcopy source such

as a paper map or a plan. On-screendigitizing is the creation of a spatial

dataset by tracing over features

Displayed on a computer monitor

with a mouse. In both cases, the newly

created dataset picks up the spatial

reference of the source document.

The following describe two differenttypes of digitizing methods:

1. Manual digitizing

Manual digitizing using a digitizing tablet has been widely used. With this method, the operator

manually traces all the lines from his hardcopy map using a pointer device and create an

identical digital map on his computer. A line is digitized by collecting a series of points

along the line.


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Digitizer

di iti th t d i f t ti ti l i f ti f d h t h


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digitizers are the most common device for extracting spatial information from maps and photographs

the map, photo, or other document is placed on the flat surface of the digitizing tablet

Problems with digitizing maps

arise since most maps were not drafted for the purpose of digitizing

paper maps are unstable: each time the map is removed from the digitizing table, the

reference points must be re-entered when the map is affixed to the table again

if the map has stretched or shrunk in the interim, the newly digitized points will be slightly

off in their location when compared to previously digitized points

errors occur on these maps, and these errors are entered into the GIS database as well

the level of error in the GIS database is directly related to the error level of the source maps

maps are meant to display information, and do not always accurately record locational

information

for example, when a railroad, stream and road all go through a narrow mountain pass, the

pass may actually be depicted wider than its actual size to allow for the three symbols to be

drafted in the pass discrepancies across map sheet boundaries can cause discrepancies in the total GIS database

e.g. roads or streams that do not meet exactly when two map sheets are placed next to each

other

user error causes overshoots, undershoots (gaps) and spikes at intersection of lines diagram

user fatigue and boredom

for a complete discussion on the manual digitizing process, see Marble et al, 1984

Editing errors from digitizing

some errors can be corrected automatically

small gaps at line junctions

overshoots and sudden spikes in lines

error rates depend on the complexity of the map, are high for small scale, complex maps
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Batch Vectorization


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Error induced by data cleaning


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Mismatches of adjacent spatial data

sources that require rubber-sheeting


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How To Use GIS

1) Mapping Where Things Are

Mapping where things are lets you find places that have the features you are looking

for and to see where to take action.

Find a featurePeople use maps to see where or what an individual feature is.Finding patternsBy looking at the distribution of features on the map instead of

just an individual feature, you can see patterns emerge.

For example, a catalog company selling children's clothes would want to find ZIP

Codes not only around their store, but also those ZIP Codes with many young

Families with relatively high income.

2) Mapping Quantities

People map quantities, such as where

the most and least are, to find placesthat meet their criteria and take action,

or to see the relationships between

places. This gives an additional level

of information beyond simply mapping

the locations of features.


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This map from the Silent Spring Institute of Newport, Massachusetts, shows the number

of breast cancer cases in Cape Cod relative to land use. The map is used to analyze

whether use of pesticides or other toxic chemicals may have contributed to the number

of cases.

Or, public health officials might

want not only to map physiciansbut also to map the numbers of

physicians per 1,000 people in

each census tract to see which areas are

Adequatel served and which are not.

3) Mapping Densities

While you can see concentrations bysimply mapping the locations of features,

in areas with many features it may be

difficult to see which areas have a

higher concentration than others.

A density map lets you measure the

number of features using a uniform unit,

such as acres or square miles, so you can clearlysee the distribution. Mapping density is especially

useful when mapping areas, such as census tracts

or counties, that vary greatly in size. on maps showing

the number of people per census tract, the larger

tracts might have more people than smaller ones. But some smaller tracts might have more

people per square milea higher density.


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4) Finding What's Inside

Use GIS to monitor what is happening

and to take specific action by mapping what is inside a specific area. For example, a district

attorney would monitor drug-related arrests to find out if an arrest is within 1,000 feet of a

schoolif so, stiffer penalties apply

5) Mapping Change

Map the change in an area to anticipate future conditions,

decide on a course of action, or to evaluate the results of

an action or policy.

1) By mapping where and how things move over a period

of time, you can gain insight into how they behave.For example, a meteorologist might study the paths of

hurricanes to predict where and when they might occur

in the future.

2) Map change to anticipate future needs. For example,

a police chief might study how crime patterns change from

month to month to help decide where officers shouldbe assigned.

3) Map conditions before and after an action or event to see the impact. A retail analyst might

map the change in store sales before and after a regional ad campaign to see where the

advertisements were most effective.


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Data in GIS

Using Geographic Data

A GIS stores information about the world as a collection of themed layers that can be used

together. A layer can be anything that contains similar features such as customers, buildings,

streets, lakes, or postal codes.

This data contains either an explicit geographic reference, such as a latitude and longitudecoordinate, or an implicit reference such as an address, postal code, census tract name, forest

stand identifier, or road name.

To work, a GIS requires explicit references. A GIS can create these explicit references from

implicit references by an automated process called "geocoding," or tying something like an

address to a specific point on the earth.

Why is data important?To create maps using GIS, you need good data. For example, if you are trying to see the

locations of your customers, you will use your database of customer addresses to make that

map. You need to ensure those addresses are correct for the map to be useful.

Data Types and Models

Data for a GIS comes in three basic forms, all of which are demonstrated in the map to the

right:

Vector data.Tabu lar data.

Raster data.


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Basic Data Models (Graphics)

There are two types of GIS Data Models:(models used for graphic representation of geographic space)

1. Vector

2. Raster

Note: A database structure need seldom be made to suit a data model. But a

well prepared data model is vital for a successful GIS analysis.


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The diagram below shows how real-world objects can be represented on acomputer monitor by x,y coordinates.

The coordinate pairs 1,5 3,5 5,7 8,8 and 11,7 represent a line (road)

The coordinate pairs 6,5 7,4 9,5 11,3 8,2 5,3 and 6,5 represent a polygon(lake).

The first and last coordinates of the polygon are the same; a polygon

always closes.

Vector Models

R t M d l


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Raster Models

Raster - from the Greek word meaning "to rake"

Quantizes or divides space into discrete packets (cells),

each representing a part of the whole

Cells are of equal size square, rectangular, hexagon,

triangles

Loose the ability to represent exact locations (e.g., point

represented as single cell)

Zero dimensional object rep. with 2D feature

Lines represented as a series of connected cells

Multiple cells joined at edges or corners, usually withonly 1 or 2 neighbors, 1D objects represented in 2D

Areas represented as a series of connected cells

2D objects represented in 2D, cells distort area and

shape - stairs-stepped appearance


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Raster Models-continue

Two general ways of associating attribute data with

raster entities 1. store an attribute for every grid cell

problem is redundancy in storage

2. link cells to RDBMS

Permits more than one attribute to be associated for asingle cell

Only have to store attributes once

Cell value linked to attribute table

Essentially many to one - "many cells being linked to one

record in separate attribute table"


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Generic structure for a grid

Rows

Columns

Gridcell

Grid extent

Resolution


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CELLS: a representation of geographic databased on rows and columns (e.g.. continuoussurface data such as elevation or temperature, and

categorical representations derived from vector data)

PIXELS: a group of independent points with acolor value but no other associated data (e.g..scanned documents, orthophotography, satellite images)

Geographic Representations

Like the vector data model, the raster data model can representdi t i t li d f t


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discrete point, line and area features.

A point feature is represented as a value in a single cell, a linearfeature as a series of connected cells that portray length, and an areafeature as a group of connected cells portraying shape.


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Because the raster data model is a regular grid, spatial relationshipsare implicit. Therefore, explicitly storing spatial relationships is notrequired as it is for the vector data model.

Vector Models


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Features represented in basically the same way as an

analog map, permits more precise representation than

raster model, permits "empty space, variations of thevector model

Spaghetti models

Simplest of vector data structures

Does not explicitly store spatial relationships(topology), essentially X,Y coordinates, and which should

be connected by lines

Doesnt really "know" if points and connected lines form

a line entity or poly entity Topological models

Recognizes the concept of an entity

Stores spatial relationship information explicitly

associated with each entity, most common in GIS

Feature Geometry


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Feature Geometry

To eep trac o many eatures, eac s ass gne a un que ent cat onnumber or tag.


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number or tag.

Then, the list of coordinates for each feature is associated with thefeatures tag.

The objects you see in a vector theme are actually saved in the theme

table


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Vector Representation


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Vector to Raster


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Raster Representation


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The mixed pixel problem

W GW

W W G

W W G

W GG

W W G

W G G

W GE

W E G

E E G

Water dominates Winner takes all Edges separate


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Vector Vs. Raster

Vector Raster Compact data

structure - littlestorage space

greater storage needed

Topology more easily

maintained (lines have

direction)

Topology difficult

Arcs more

aesthetically pleasing

Grids not very

aesthetic

Data structure morecomplex

Data structure moresimple

Better geographic

specificity

Limited geographic

specificity (due to

resolution)

DATA MODEL OF RASTER AND VECTOR


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DATA MODEL OF RASTER AND VECTOR

REAL WORLD1 2 3 4 5 6 7 8 9 10

1

2

3

4

5

6

7

8

9

10

GRID RASTER VECTOR


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RASTER DATA MODEL

derive from formulation that real world - it has spatial

elements and objects fills those elements

real world is represented with uniform cells

list of cells is a rectangle

cell comprises of triangles, hexagon and highercomplexities

a cell reports its own true characteristics

per units cell does not represent an object

an object is represented by a group of cells


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Pond

Lake

Pond

Lake

1 1 0

11

1 1 1

11 1

22

22

2

2

11

0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0 00 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

Reality - Hydrography

Reality overlaid with a grid

Resulting raster

Creating a Raster

0 = No Water Feature1 = Water Body

2 = River


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VECTOR DATA MODEL

derived from the formulation of spatial concepts that

emphasize on real world objects geometry primitives of vector data model are point, line

and polygon

objects can be built from these primitives

object location determined by represented location point uniqueness of vector data model lies in its management

and storage of data geometry primitives

spaghetti model

topology model


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VECTOR CHARACTERISTICS

POINT X

LINE

POLYGON


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RASTER TO VECTOR

RIVER CHANGED FROM RASTER TO VECTOR FORMAT

RIVER THAT HAS BEEN VECTORISED

ORIGINAL RIVER


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PRO AND CONS OF RASTER MODEL

pro

raster data is more affordable

simple data structure

very efficient overlay operation

cons topology relationship difficult to implement

raster data requires large storage

not all world phenomena related directly with raster

representation raster data mainly is obtained from satellite images and

scanning


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PRO AND CONS OF VECTOR MODEL

pro

more efficient data storage

topological encoding more efferent

suitable for most usage and compatible with data

good graphic presentation

cons

overlay operation not efficient

complex data structure

A look behind the scenes: Vector GIS


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A look behind the scenes: Vector GIS

data models

Spaghetti model

Topological vector model

Cardinality (this is gonna hurt!)

Break

Raster or Vector?


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Raster or Vector?

While any feature type can be represented using either model, discrete features, such as

customer locations, pole locations or others, and data summarized by area such as

postal code areas or lakes, are usually represented using the vector model.

Continuous categories, such as soil type, rainfall, or elevation,

are represented as either vectoror raster.

C. Tabular data

Tabular data is information describing a

map feature. For example, a map of

customer locations may be linked

to demographic information about thoseCustomers Tabular data for use in a GIS can

be purchased already packaged

with spatial dataor it can be found in

your own organization.

D t b
http://www.gis.com/data/spatial_data.htmlhttp://www.gis.com/data/spatial_data.html


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Databases

The I in GIS GIS are often split into two components

Coordinate information (describes object

geometry or spatial information)

Attribute information (describes other non-

spatial properties associate with it)

Often referred as tabular data as they are presentedin tabular form

Databases cont


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GIS data components - spatial & non-spatial

Databases - cont.

Bolstad, 2005

Attribute Information Presentation


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Attribute Information Presentation

In GIS, attribute information are typicallyentered, analyzed, and presented using a

database management system (DBMS)


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DBMS Functions

DBMS incorporates a special set of softwaretools to manage the GIS non-spatial tabular

data

Efficient data storage

Data retrieval

Data indexing

Data reporting


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First PC-based Database Software

Lotus 1-2-3 It combines

Graphics

Spread sheet functions Data management


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Database software...

Light Duty

Medium Duty

Heavy Duty

(Rational Rose)

Att ib t T bl D t b i A GIS


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Attribute Tables: Database in ArcGIS

Records

Fields/Attributes

Common Features in Attribute Table


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Common Features in Attribute Table

Some Facts about Attribute Table


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Some Facts about Attribute Table columns : fields/attributes

rows : records Automatic Fields:

FID and Shape fields automatically created

During Digitizing:

Length of lines Area & Perimeter of Polygons

You can add new fields and values to an existing attributetable

Attribute tables are saved in workspace as *.dbf file

You can export your new updates in attribute file in manyformats


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Examples of Selection Based on Attributes

Table queries Simple selection

AND selection

OR selection

NOT selection

Bolstad, 2005

Linking Tables


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Linking Tables

The idea of linkages between tables is central to the

relational database model

In ArcGIS, these are known as joins and links

Common values for common items are used to associate

records from one table to another

Common Field

bl


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Joining Tables

k bl ( )


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Linking Tables (Cont.)

Right-click the datalayer

Select Joins and Relates

> Join Select the choices as

shown in picture.

This will join the

gageusgstable to the

idhucstable, based on

the HUCfield.

d i i O i i G S


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Advance Joining Option in GIS

Selecting the Right Data


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g g

As you search for data for your GIS, you will go through a process of making a wish list and

investigating data that meets your criteria. Following are the most important issues you will

need to consider to determine which data you need.

1- What do you want to do with the data?

Do you want to draw maps or do a certain type of analysis? Do you want to match customers

to street addresses or to telephone exchange areas? Do you simply want to draw an accurate

street map, or do you want to use the GIS software to develop delivery routes?

Consider carefully how you answer these questions because the answers will likely governyour answers to the following questions. Take into account your medium- or long-term goals

as well as those you want to accomplish now.

2- What are the specific geographic features you need?

To gain the most understanding from your GIS, determine the level of detail required from

your data. For example, do you want all streets or major highways? If so, at what level of

generalizationmajor highways at a "local" scale, such as 1:24,000, or at a "national"

scale, such as 1:3,000,000. Even for a seemingly simple feature such as streets, you may

need to decide how you want them represented (centerlines, double-lined streets, or

connected routes).

3- What attributes of those features do you need?

U i t t l d di l ill h t d t i h th


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Using streets as an example, depending on your goals you will have to determine whether

you need none, some, or all of the following attributes: street name, route number, road

class, road surface class, address ranges, traffic volume, and under- or overpass.

4- What is the geographic extent of your area of interest?

Data can be acquired for areas as small as a ZIP Code or census block or as large as theentire world. You will need to determine the size of the area for which you need data.

5- What is the level of geography you want to examine within your area of interest?

Your area of interest can often be broken down into smaller areas. Within a state, for

example, you may want to examine statistics by census tract, block group, ZIP Code, or

cable TV area.

6- How current must the data be?

For some applications, such as land use planning using remotely sensed imagery or aerialphotography, obtaining the latest data available is critical. For other applications, data that

was collected a year or two before may be adequate.

7- What GIS software will you be using?

The answer to this question may affect the data format you select.

8- When do you need the data?

Many "off-the-shelf" data sets can be acquired in a couple of business days, but if youneed customized data sets, plan ahead. Orders that require customization may take up to

several weeks to prepare and deliver.

9- Will you need periodic data updates and, if so, how frequently?

Determine if complete replacements of the data are preferred or if you require transactional

updates (changes only).

Maps and Maps Analysis

(C h )


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(Cartography)

1. Maps and CartographyINTRODUCTION

maps are the main source of data for GIS

the traditions of cartography are fundamentally important to GIS

GIS has roots in the analysis of information on maps, and overcomes many of the limitations of manualanalysis

This chapter about cartography and its relationship to GIS - how does GIS differ from cartography,particularly automated cartography, which uses computers to make maps?

WHAT IS A MAP?

Definition

according to the International Cartographic Association, a map is: a representation, normally to scale and on a flat medium, of a selection of material or abstract featureson, or in relation to, the surface of the Earth

Maps show more than the Earth's surface

the term "map" is often used in mathematics to convey the notion of transferring information from one formto another, just as cartographers transfer information from the surface of the Earth to a sheet of paper

the term "map" is used loosely to refer to any visual display of information, particularly if it is abstract,generalized or schematic

Cartographic abstraction

production of a map requires:

selection of the few features in the real world to include

classification of selected features into groups (i.e. bridges, churches, railways)

simplification of jagged lines like coastlines

exaggeration of features to be included that are to small to show at the scale of the map

symbolization to represent the different classes of features chosen

2. Types of maps

in practice we normally think of two types of map:


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topographic map - a reference tool, showing the outlines of selected natural and man-madefeatures of the Earth

often acts as a frame for other information

"Topography" refers to the shape of the surface, represented by contours and/or shading,

but topographic maps also show roads and other prominent features thematic map - a tool to communicate geographical concepts such as the distribution of

population densities, climate, movement of goods, land use etc.

topographic map thematic map

Thematic maps in GIS

several types of thematic map are important in GIS:


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a choropleth map uses reporting zones such as counties orcensus tracts to show data such as average incomes, percentfemale, or rates of mortality

the boundaries of the zones are established independently ofthe data, and may be used to report many different sets ofdata

an area class map shows zones of constant attributes, such asvegetation, soil type, or forest species

the boundaries are different for each map as they aredetermined by the variation of the attribute being mapped,e.g. breaks of soil type may occur independently of breaks ofvegetation

Chl l th M G d t d C l


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Chloropleth MapGraduated Colors

Easy to see patterns

Hard to go from colors to values

Characteristics of maps


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maps are often stylized, generalized or abstracted, requiringcareful interpretation

usually out of date show only a static situation - one slice in time

often highly elegant/artistic

easy to use to answer certain types of questions:

how do I get there from here?

what is at this point?

difficult or time-consuming to answer other types:

what is the area of this lake?

what places can I see from this TV tower?

what does that thematic map show at the point I'm interestedin on this topographic map?

l f


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Scale of a map

All maps are reduction in size of the Earth.The scale is the ratio of distances on the map to the same

distance on the ground.

It is generally expressed as 1: 100,000, that is 1 cm on the

map equals to 100,000 cm on the Earth.

Large scale (ratio is a large fraction) shows small areaswith many details

Small scale (ratio is a small fraction) shows larger areaswith fewer details


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SMALL SCALE

LARGE SCALE


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LARGE SCALE

Cartography & Digitizing

Basic Concepts of Cartography


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Basic Concepts of Cartography

1) Map as Model: The Abstraction of Reality

Models are simplifications - not miniature versions of the reality.

Maps are a type of geographic model. Maps are abstraction from reality.

The Importance of MapsTo record and store informationTo analyze locational distributions and spatial patterns

To present information and communicate findings

Purpose of Cartography

Cartography is the art and science of map making.

Communication is the traditional objective.

Analysis has become an important objective with the

development of GIS.2) Basic Elements of Map Composition

A. Map Scale: Map scale defines the amount of

reduction of reality. Scale defines the precision of the

location and the level of detail Be care when using

small scale maps as input and then enlarging It is always

better to reduce a map after analysis than to enlarge it for analysis.

Scale is expressed in three primary ways:

Verbal Scale

Representative fraction (RF) 3. Graphic scale (bar)

1. Verbal Scale

Map scale is expressed as ordinary text words
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p p y

ex: 1 centimeter equals (represents) 1 meter .

2. Representative fraction (RF)

Map scale is expressed as a ratio in the same units.

ex:1:2,000 means that one inch (or one meter) on the map represents 2,000 inches (or

meters) on the ground.

3. Graphic Bar

The graphic bar places visual measure of ground distances on the map.Used on printed maps

(output of GIS) to aid in communicating the scale. Most software can automatically generate a

graphic scale.

Ex:

Remains accurate after mechanical enlargement of map, printed ratio or printed scale will be

wrong after "zooming" the page on the copy machine.

Map Scale: Small vs. Large

Small scale refers to the RF ratio. A 1:250,000 scale is small compared to a 1:2,000.The ratio

is small and the amount of reduction is large, producing a map of a large area.

Large scale means less reduction and a map covering a small area.

B. Legend

1 The reference area on a map that lists the colors symbols line patternsLegend

!


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1. The reference area on a map that lists the colors, symbols, line patterns,

shadings and other annotation used on the map, and their meanings.

The legend often includes the map's title, scale, origin, orientation

and other information.

2. The symbol key on a map used to describe a map's symbols and howthey are interpreted.

C. Direct ion

The question of what is northcan be an issue on some maps.

On the earth, true north(the direction to the North Pole) differs

from magnetic north, and the magnetic north pole moves due

to changing geophysical conditions of the earth's crust and core.

Many reference maps indicate both. Most maps we compose areoriented to true north, even though compass readings in the field

are angled to the magnetic pole. Adjustments for these compass

deviations are made routinely.

D. Sources of information and how processed

Unless it is absolutely clear from the context in which a map

appears, readers will need to know about the sources from whichthe map was derived. Often the age, accuracy, and reliability

of sources is critical to the interpretation of a map and should

be noted.

!. Donut

Railroad

Street

RGB Composite

Red: Band_1

Green: Band_2

Blue: Band_3

E. Title

The title of a map is usually one of its most essential features As such it should receive very


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The title of a map is usually one of its most essential features. As such, it should receive very

careful attention so as to match the needs of the theme and audience. The content of the title

should also be measured against other lettering applied to the map, for example in the legend

or annotations

F. ProjectionThe projection used to create a map influences the representation of area, distance, direction,

and shape. It should be noted when these characteristics are of prime importance to the

interpretation of the map.

G. CartographerThe authority lying behind the composition of a map can be of prime

importance in some situations. Most maps note the name, initials, or corporate identity of the

cartographer(s).

H. Date of production

The meaning and value of some maps--such as those relating to current affairs or


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The meaning and value of some maps--such as those relating to current affairs or

weather--are time sensitive. The reader must know when they were produced to

estimate whether to trust them or not. An out-of- date road atlas or city map can

cause tremendous frustration. Other maps are less sensitive to the passage of

time, but the date of production can still be important if, for example, better

information becomes available in the period after publication.

I. Neatlines

Neatlines or clipping lines are used to frame a map and to indicate exactly where

the area of a map begins and ends. The outer neatline of a map--its border--

helps to frame the entire map composition to draw the reader's attention to the

various elements of information. Neatlines are also used to "clip" the area of the

body of the map and of locator, and inset maps.

J. Locator maps

Some maps portray areas whose locations may be unfamiliar to readers. In such

cases, the cartographer adds a "helper" or locator map that places the body of

the map within a larger geographical context with which the reader can beexpected to be familiar.

k. Inset maps

Sometimes observations and data are so densely clustered in small sections of a

larger map that the cartographer must provide the reader with additional close-

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