introduction-overview • why use a gis? • what can a gis do...

CM3205 - 51 – GEOGRAPHIC INFORMATION SYSTEMS

Introduction-Overview

• Why use a GIS?• What can a GIS do?• How does a GIS work?• How does a GIS work?

• GIS definitions

• Spatial (coordinate) data model

• Relational (tabular) data model( )

Gary Weaver intro_gis.ppt 1


Why use a GIS?

• An extension of the paper map, but much more than a map, as you will see.• GIS uses the analytical power of the computer to complete complex tasks.• Computer's storage power to manage large data sets. p g p g g• Integration of many different types of data from many different sources.• GIS maps a variety of different data to the same coordinate space (combination).• Digital media are more stable than paper media, and easier to distribute via the net.Digital media are more stable than paper media, and easier to distribute via the net.

• Faster and easier update. • Creation and use of "one-time" maps. • Tailor-made mapsTailor made maps.

• Elimination of some user bias.

• GIS brings new tools for thinking differently about geographic data• GIS brings new tools for thinking differently about geographic data.



What can a GIS do?

• Generically• Locate geographic features based on properties. • Identify and analyze properties of geographic features based on location.

• Specifically• Estimate economic effects of land-use regulation. • Determine the optimal locations of new businesses• Determine the optimal locations of new businesses.• Generate optimal routing and scheduling delivery and repair services. • Determine the ground area covered by a new cellular phone network. • Delineate watershed boundaries for estimates of sedimentation effects. • Predict vegetation types based on elevation, slope, and aspect. • Predict landslide hazard for harvest units. • Locate natural areas that need protection.• Make colorful and interesting maps.



The GIS Model: Examples

•roadsHere we have three layers or themes:--roads,

•longitude•longitude

,--hydrology (water),--topography (land elevation)

They can be related because precise geographic coordinates are recorded for each theme.

•hydrologyLayers are comprised of two data types

•longitudey p yp

Spatial data which describes location (where)Attribute data specifying what, how much, and when

Layers may be represented in two ways:

•topography

y y p y1. in vector format as points and lines2. in raster(or image) format as pixels

All geographic data has 4 properties:


•longitude

g g p p pprojection, scale, accuracy and resolution


Examples of what a GIS can do

• Example 1: Where is a given feature or set of features? Where is Aurora Ave N?




• Example 2: Where is a particular location?Where is the corner of Aurora Ave N & N 50th St?




• Example 3: What parcels will be affected by a road resurfacing project?Which parcels are within ½ mi of Aurora between N 35th & N 50th?




• Example 4: Where are areas that meet a given complex set of criteria? What parts of the forest are located:

• on > 30% slope?

• closer than 100 ft to a stream, and• farther than 50 ft from a road,



Examples of GIS maps

topographic mapping




orthophoto image maps




surface drapes & 3-D modeling




classified thematic mapping




research documentation



How does GIS work?

bi i f d• Combination of coordinate data

and

tabular dataeach feature has a record



GIS definitions

• "A system of hardware, software, and procedures designed to support the capture, management, manipulation, analysis, modeling and display of spatially-referenced data for solving complex planning and management problems."

• A working GIS integrates five key components:

f• hardware,

• people, and• data, • software,

• methodsp p



Spatial Data Model

GIS are driven by spatial data - 2 basic spatial data models exist

• VectorTh f d l f GIS i h ll hi f• The fundamental concept of vector GIS is that all geographic features in the real work can be represented either as:

• points or dots (nodes): trees, poles, fire plugs, airports, cities• lines (arcs): streams, streets, sewers,( ) , , ,• areas (polygons): land parcels, cities, counties, forest, rock type • Because representation depends on shape, ArcGIS refers to files

containing vector data as shapefilesR t• Raster

• area is covered by grid with (usually) equal-sized, square cells• attributes are recorded by assigning each cell a single value based on

the majority feature (attribute) in the cell, such as land use type.j y ( ) , yp• Image data is a special case of raster data in which the “attribute” is a

reflectance value from the geomagnetic spectrum• cells in image data often called pixels (picture elements)



Vector Data Model

• Characteristics of the vector data model:

• Features positioned accurately• Features positioned accurately

• Shape of features represented correctly

• Features represented discretely (no fuzzy boundaries)

• Complex data structure (especially for •pointComplex data structure (especially for polygons) •line

•polygon



Vector Data Model

Points: represent discrete point features



Vector Data Model

Lines: represent linear features



Vector Data Model

Lines: represent linear features

• Lines start and end at nodes• line #1 goes from node #2 to node #1

• Vertices determine shape of line


Vertices determine shape of line_


Vector Data Model

Polygons: represent bounded areas



Vector Data Model


• Polygon #2 is bounded by lines 1 & 2• Line 2 has polygon 1 on left and polygon 2 on right



Vector Data Model


• complex data model• “arc/node topology”• arc/node topology



Vector Data Model

Types (formats) of vector data available in ArcView

• ArcGIS shapefilesArcGIS shapefiles

• ArcInfo coverages and libraries

• CAD files (AutoCAD DWG, DXF;Microstation DGN)

• StreetMap files

• Spatial Database Engine (SDE) data

• ASCII point coordinate data



Vector Data Model

• A vector data format

Shapefiles

A vector data format

• Preferred in ArcGIS• Draws fast• Fully editable in ArcGIS

• Simple in structure

• Does not use arc-node topology• “Connected” lines do not necessarily share a common node

Adj t l d t h b di• Adjacent polygons do not share common bounding arcs• Data sets are either point or line or polygon



Vector Data Model

• A older commonly found format

ArcInfo coverages

A older commonly found format

• Data model more complex

• Draws more slowly in ArcGIS

• Coordinate data not editable in ArcGIS

• Can be used in both ArcGIS and ArcInfo

P l hi• Polymorphic

• Problematic file structure (more on this later in the term)



Vector Data Model

• CAD data are very common (industry standard)

AutoCAD & Microstation CAD drawing data

• CAD data are very common (industry standard)

• DXF, DWG, and DGN formats supported in ArcGIS

• Coordinate data not editable in ArcGIS

• Frequently contain “sloppy” dataq y ppy• No enforced topology rules• Gaps in data

• Frequently contain little or no useful attribute data



Vector Data Model

• Easy to obtain from a variety of sources

ASCII coordinate data

y y• GPS• Traverse• Direct reading from maps

• OS, architecture, and application independent



Raster Data Model

• Rectangular grid of square cells

Characteristics of the raster data model:

g g q

• Shape of features generalized by cells

• Contin o s (s rface) data represented easil• Continuous (surface) data represented easily

• Simple data structure



Raster Data Model

Wi d d

Raster data are good at representing continuous phenomena

• Wind speed

• Elevation, slope, aspect

• Chemical concentration

• Likelihood of existence of a certain speciesLikelihood of existence of a certain species

• Electromagnetic reflectance (photographic or satellite imagery)



Raster Data Model

• origin is set explicitly

Raster spatial data model

• cell size is known

ll f• cell references (row/column locations)are known

• cell values are referencedto row/column location

• values represent numerical phenomena orindex codes for non-


numerical phenomena


Raster Data Model

A few different types of raster data

• digital orthophotodigital orthophoto

• digital elevation model (DEM)



Relational Database Model & Attribute Data Structures

• The “where” of GIS is determined by coordinate (map) data structures, but …

• The “what” of GIS is determined by tabular (relational database) data structures

• Thus, tabular data are just as important as coordinate data




Attribute data are stored in database tables.

• Tables are composed of:

• fields

and

d• records




You may already be familiar with relational databases

• dBase

• rBaserBase

• Access

• Excel (database functionality)

• Oracle, INFORMIX, INGRES, SQL Server

• INFO (in ArcInfo)




ArcGIS uses tabular data formats from dBase, ASCII text, and INFO files

• tables are stored on the drives as

• .dbf,.dbf,

• .txt, or

• in INFO directories




Tables can be linked and joined (“related”) by use of common values in fields




V

Different types of attribute tables in ArcView

• Vector• point attribute tables• polygon attribute• line attribute• line attribute

• node attribute* • text attribute*text attribute• route & event tables*

• RasterRaster• value attribute


* in ArcInfo coverage data only

introduction-overview • why use a gis? • what can a gis do...

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