7/28/2019 What is GIS(1)

1/26

A friendly introduction to

Geographic InformationSystems

Marc Albrecht

University of Nebraska at Kearney

Department of Biology

mailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edumailto:albrechtm@unk.edu

7/28/2019 What is GIS(1)

2/26

Context: Why GIS?

Many of the issues in our world have acriticalspatial component!

Land management Property lines, easements, right of ways

Data on land values, taxation, assessment

Business site selection, advertising Proximity of our land to other facilities

(pollution, hunting, municipal, federal, state)

I dont know whats over that hill is a common

problem. What is adjacent to the land we are using?

7/28/2019 What is GIS(1)

3/26

The Space on Earth

The Earth isfinite!

If not now, within our lifetimes there may be

no natural ecosystems. Land managers, natural resource workers,

and politicians are and will continue to make

decisions about biological systems. Good information and tools are needed todo this.

7/28/2019 What is GIS(1)

4/26

Enter GIS

A computer-basedtool for holding,

displaying, andmanipulating hugeamounts of spatial

data.

7/28/2019 What is GIS(1)

5/26

Outline of Presentations

What is GIS? Presentation

Part I: Maps and Mapping

Part II: Some GIS Operations

GIS Resources and Projects Presentation

Part III: Where do I get data?

Part IV: Ongoing Programs, other software

Part V: Project Ideas and Examples

7/28/2019 What is GIS(1)

6/26

Part I: Map Concepts

What is a map?

What are some properties of maps?

Vector vs. raster: two digital mappingmethods

Maps reflect the databases we create

Mapping the third dimension: examplesof 3-D maps

7/28/2019 What is GIS(1)

7/26

Representing the World:Projections

3-D to 2-D (at first)

Projections change a roundworld into a flat one.

7/28/2019 What is GIS(1)

8/26

What is in a picture?

Example: The Mercator projectionhas straight meridians & parallelsthat intersect at right angles, asopposed to the Robinson projection.

Mercator preserves area only at theequator and at two standard parallelsequidistant from the equator.

The Mercator projection is often used for

marine navigation as all straight lines onthe map are lines of constant azimuth.

Any one projection cannotsimultaneously preserve all thesequalities of the world: shape, area,

direction, and distance.

7/28/2019 What is GIS(1)

9/26

Projections and Metadata There are dozens of types of projects, and about six that are

commonly used.

People choose a projection based on which qualities they most

want to preserve in a map. Sites such as Dr. Danas andNational Geographic discuss projections in more detail

The point is that you need to know where your data (maps)come from and information about it. This is called METADATA

data about the data. Good metadata includes who collectedthe data, when, to what accuracy, how the data are projected,and the collectors contact information.

You should be a responsible GIS user and keep track of your

metadata!

http://www.utexas.edu/depts/grg/gcraft/notes/mapproj/mapproj.htmlhttp://magma.nationalgeographic.com/2000/exploration/projections/index.cfmhttp://magma.nationalgeographic.com/2000/exploration/projections/index.cfmhttp://www.utexas.edu/depts/grg/gcraft/notes/mapproj/mapproj.html

7/28/2019 What is GIS(1)

10/26

The Projection Problem When working with GIS systems you have to know about

projections in general and what projection the different datayou are using are in.

This is a metadata issue again.

It is possible to transform data from one projection to another, but iseasier especially when starting out to have the different data layersin same projection when you obtain them! Agencies are generallyhelpful about doing this step for you if asked.

Another Problem are Datums basically mathematicaldescriptions of the Earths size and shape. If either theprojection or the datums of your map layers are not identical:

YOUR MAP LAYERS WILL NOT LAY ON TOP OF EACH

OTHER, BUT RATHER BE SHIFTED INTO DIFFERENTAREAS!! This is embarrassing and frustrating.

7/28/2019 What is GIS(1)

11/26

This is what happens whenprojections mix!

Notice theboundary lines

do not line up Points that are

placed on thewrong

projection willbe misalignedas well

7/28/2019 What is GIS(1)

12/26

Raster vs. Vector: types of GISmap representation

Vector vs. Raster

Two basic ways that spatial data can berepresented

Raster:

Data represented by pixels withvalues, creating a grid

Allows certain types of operationsnot possible with vector data

Map algebra is possible with multiple

data layers creating index maps

Vector:

Data stored as points, lines, andpolygons

Uses less memory than raster format Does not loose positional accuracy

7/28/2019 What is GIS(1)

13/26

How is all this done? GIS stores data in a

relational databasestructure(3-Dspreadsheets)

e.g. employee names linked tostore number, store numberlinked to shipment arrival

any data can be linked by acommon attribute to any otherdata

Example shown here is alist of counties (geographicdata) by income code(demographic data)

7/28/2019 What is GIS(1)

14/26

High End 3-D Representation

Surfaces are made fromTriangular IrregularNetworks (TIN) that

interpolate 3-D surfacesfrom 2-D contourvalues.

Uses:

Hydrology: surface andunderground flows

Line-of-Sight analysis

Pollution Plume tracking

Customer analysis

Soil erosion potential

7/28/2019 What is GIS(1)

15/26

3-D Rendering Example

Beaty, NV

USGS 7.5

Minute quad in3-D

A 3-Drenderingof theterrain

Elevationmeasurements canbe easily converted

into 3-D.Such elevationaldata are collectedregularly by federal

and state agencies. These data canbe downloaded/ordered at little

or no cost.

7/28/2019 What is GIS(1)

16/26

How many data points are contained in this image? Thousands? More?

Even without statistical measurement (which can be done) the pattern ofpollution can be seen. Location and density of wells is also clear.

Line of sight analysis allows us to determine where to put a house or powerplant where it could or could not be seen from major roads. Notice the roadsactually track up the hills on the right side of the image.

7/28/2019 What is GIS(1)

17/26

Part II. What can GIS do?

Some general types of GIS operations are listed onthe next few slides

Many more are possible than are shown here and moreare being created every day

Extensions and scripts created by users(http://www.esri.com/arcscripts)

Third-party and government developers make softwareplug-ins for specific uses (eg. EPAs BASINS software)

http://www.esri.com/arcscriptshttp://www.epa.gov/ost/BASINS/http://www.epa.gov/ost/BASINS/http://www.esri.com/arcscripts

7/28/2019 What is GIS(1)

18/26

1. Proximity Analysis Two or more data layers are overlaid

GIS creates buffers around features on a particular layer

This allows analyses such as flood zone delineation and

features near a route such as hotels along a bike route.

7/28/2019 What is GIS(1)

19/26

2. Query and Overlay Analyses Query building is a data exploration operation

Example statement: ([acres] > 500 AND [age] > 55)

This would highlight all land parcels of greater than 500 acres owned by

people older than 55 years old in a data set loaded into the GIS.

Map algebra with raster data, in this type of operationmathematical operations are done on each pixel of multipledata layers. This results in a new data layer that is calculatedfrom all the input layers.

7/28/2019 What is GIS(1)

20/26

3. Spatial Analysis

Raster data can alsobe used to createsurfaces

Other raster datauses:

Density analysis

Proximity analysis Least-cost paths

Line-of-sight

Hydrology analysis

7/28/2019 What is GIS(1)

21/26

Part II: Data Examples

Here is Atlanta

Highways

Roads Census Tracts

7/28/2019 What is GIS(1)

22/26

Close up of downtown

Map contains data for eachstreet

Each address in the city can begeocoded that is its locationestimated in a systematic way

Length of each street segment

- block Streets can be sorted by

length, name, income, homevalue, race, age - all provided

by the Census Bureau (TIGER)

7/28/2019 What is GIS(1)

23/26

Atlanta Example Hypothetical population

of opossums.

Data can be sorted by

attribute, such as sex,females are yellow inthis example

Hmmm, why aremales found closer topopulated areas?

We do not knowbuthow else would wediscover the pattern?

7/28/2019 What is GIS(1)

24/26

Atlanta

Same population nowreclassified by someother attribute.

a genetic marker? age?, size?

Other operations: I can make a chart of any of

the attributes. I can compute density of

points to see where theanimals are most clustered

Measure distances between

individual locations

7/28/2019 What is GIS(1)

25/26

7/28/2019 What is GIS(1)

26/26

Thanks for viewing this presentation. Please email me with anycomments or questions you have.

If you want to learn more about doing your own GIS projects, and morecapabilities of GIS, please view the presentation GIS Resources and

Projects in this folder. A number of the images and figures in this presentation are reproduced with

permission from the ESRI website. Please visit there to learn more!

Other images used with the permission as stated of Peter H. Dana, TheGeographer's Craft Project, Department of Geography, The University of Texasat Austin. All commercial rights reserved. Copyright 1995 Peter H. Dana.

mailto:albrechtm@unk.eduhttp://www.esri.com/http://www.esri.com/mailto:albrechtm@unk.edu