What is GIS?What is GIS?

A friendly introduction to A friendly introduction to Geographic Information Geographic Information

SystemsSystemsWith thanks toWith thanks toMarc AlbrechtMarc Albrecht

University of Nebraska at KearneyUniversity of Nebraska at Kearney

Context: Why GIS?Context: Why GIS? Many of the issues in our world have a Many of the issues in our world have a

criticalcritical spatial component!spatial component!– Land managementLand management– Property lines, easements, right of waysProperty lines, easements, right of ways– Data on land values, taxation, assessmentData on land values, taxation, assessment– Business site selection, advertisingBusiness site selection, advertising– Proximity of Proximity of ‘‘ourour’’ land to other facilities land to other facilities

(pollution, hunting, municipal, federal, state)(pollution, hunting, municipal, federal, state) ““I donI don’’t know whatt know what’’s over that hills over that hill”” is a common is a common

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

The Space on EarthThe Space on Earth The Earth isThe Earth is finite!finite!

– If not now, within our lifetimes there may If not now, within our lifetimes there may be be no natural ecosystemsno natural ecosystems. .

– Land managers, natural resource workers, Land managers, natural resource workers, and politicians are and will continue to and politicians are and will continue to make decisions about make decisions about biological systemsbiological systems. .

– Good Good informationinformation and and toolstools are needed to are needed to do this. do this.

Enter GISEnter GIS A computer-A computer-

based tool for based tool for holding, holding, displaying, and displaying, and manipulating manipulating huge amounts of huge amounts of spatial data.spatial data.

Outline of PresentationsOutline of Presentations ““What is GIS?What is GIS?”” Presentation Presentation

– Part I: Maps and MappingPart I: Maps and Mapping– Part II: Some GIS OperationsPart II: Some GIS Operations

““GIS Resources and ProjectsGIS Resources and Projects”” Presentation Presentation– Part III: Where do I get data?Part III: Where do I get data?– Part IV: Ongoing Programs, other softwarePart IV: Ongoing Programs, other software– Part V: Project Ideas and ExamplesPart V: Project Ideas and Examples

Part I: Map ConceptsPart I: Map Concepts What is a map?What is a map?

– What are some properties of maps?What are some properties of maps?– Vector vs. raster: two digital mapping Vector vs. raster: two digital mapping

methodsmethods Maps reflect the databases we createMaps reflect the databases we create Mapping the third dimension: Mapping the third dimension:

examples of 3-D mapsexamples of 3-D maps

Representing the World: Representing the World: ProjectionsProjections 3-D to 2-D (at first)3-D to 2-D (at first)

– Projections change a Projections change a round world into a flat round world into a flat one. one.

What is in a picture?What is in a picture? Example: The Mercator projection Example: The Mercator projection

has straight meridians & parallels has straight meridians & parallels that intersect at right angles, as that intersect at right angles, as opposed to the Robinson projection. opposed to the Robinson projection. – Mercator preserves area Mercator preserves area onlyonly at the at the

equator and at two standard parallels equator and at two standard parallels equidistant from the equator. equidistant from the equator.

– The Mercator projection is often used The Mercator projection is often used for marine navigation as all straight for marine navigation as all straight lines on the map are lines of constant lines on the map are lines of constant azimuth. azimuth.

– Any one projection cannot Any one projection cannot simultaneously preserve all these simultaneously preserve all these qualities of the world: qualities of the world: shapeshape, , areaarea, , directiondirection, and , and distancedistance..

Projections and Projections and MetadataMetadata There are dozens of types of projections, and about six There are dozens of types of projections, and about six

that are commonly used.that are commonly used. People choose a projection based on which qualities People choose a projection based on which qualities

they most want to preserve in a map. Sites such as they most want to preserve in a map. Sites such as National Geographic discuss projections in more detailNational Geographic discuss projections in more detail

The point is that you need to know where your data The point is that you need to know where your data (maps) come from and information about it. This is (maps) come from and information about it. This is called called METADATAMETADATA – data about the data. Good – data about the data. Good metadatametadata includes who collected the data, when, to includes who collected the data, when, to what accuracy, how the data are projected, and the what accuracy, how the data are projected, and the collectorcollector’’s contact information.s contact information.

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

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

projections in general and the projections of the different projections in general and the projections of the different data sets that you are using. data sets that you are using. – This is a metadata issue again.This is a metadata issue again.– It is possible to transform data from one projection to another, but is It is possible to transform data from one projection to another, but is

easier – especially when starting out – to have the different data easier – especially when starting out – to have the different data layers in the same projection when you obtain them! Agencies are layers in the same projection when you obtain them! Agencies are generally helpful about doing this step for you if asked. generally helpful about doing this step for you if asked.

Another Problem are Datums – basically mathematical Another Problem are Datums – basically mathematical descriptions of the Earthdescriptions of the Earth’’s size and shape. If either the s size and shape. If either the projection or the datums of your map layers are not projection or the datums of your map layers are not identical:identical:

YOUR MAP LAYERS WILL NOT LAY ON TOP OF EACH YOUR MAP LAYERS WILL NOT LAY ON TOP OF EACH OTHER, BUT RATHER BE SHIFTED INTO DIFFERENT OTHER, BUT RATHER BE SHIFTED INTO DIFFERENT AREAS!! AREAS!! This is embarrassing and frustrating.This is embarrassing and frustrating.

This is what happens when This is what happens when projections mix!projections mix!

Notice the Notice the boundary boundary lines do not lines do not line upline up

Points that are Points that are placed on the placed on the wrong wrong projection will projection will be misaligned be misaligned as well as well

Raster vs. Vector: types of Raster vs. Vector: types of GIS map representationGIS map representation

VectorVector vs. vs. RasterRaster Two basic ways that spatial data can be Two basic ways that spatial data can be

representedrepresented Raster:Raster:

– Data represented by cells with Data represented by cells with values, creating a gridvalues, creating a grid

– Allows certain types of operations Allows certain types of operations not possible with vector datanot possible with vector data

– Map algebra is possible with multiple Map algebra is possible with multiple data layers – creating index mapsdata layers – creating index maps

Vector: Vector: – Data stored as points, lines, and Data stored as points, lines, and

polygonspolygons– Uses less memory than raster formatUses less memory than raster format– Does not lose positional accuracyDoes not lose positional accuracy

How is all this done?How is all this done? GIS stores data in aGIS stores data in a

relational database relational database structurestructure ( (‘‘3-D 3-D spreadsheetsspreadsheets’’))– e.g. employee names linked e.g. employee names linked

to store number, store to store number, store number linked to shipment number linked to shipment arrivalarrival

– any data can be linked by a any data can be linked by a common attribute to any common attribute to any other data other data

Example shown here is a Example shown here is a list of counties (geographic list of counties (geographic data) by income code data) by income code (demographic data)(demographic data)

High End 3-D High End 3-D RepresentationRepresentation

Surfaces are made Surfaces are made from Triangular from Triangular Irregular Networks Irregular Networks (TIN) that interpolate (TIN) that interpolate 3-D surfaces from 2-D 3-D surfaces from 2-D contour values. contour values.

Uses: Uses: – Hydrology: surface and Hydrology: surface and

underground flowsunderground flows– Line-of-Sight analysisLine-of-Sight analysis– Pollution Plume trackingPollution Plume tracking– Customer analysisCustomer analysis– Soil erosion potentialSoil erosion potential

3-D Rendering Example3-D Rendering Example

Beaty, NV

USGS 7.5 Minute quad in 3-D

A 3-D rendering of the terrain

Elevation measurements can be easily converted into “2.5-D.”Such elevational data are collected regularly by federal and state agencies.

These data can be downloaded/ ordered at little or no cost.

How many data points are contained in this image? Thousands? More?How many data points are contained in this image? Thousands? More?– Even without statistical measurement (which can be done) the pattern of Even without statistical measurement (which can be done) the pattern of

pollution can be seen. Location and density of wells is also clear.pollution 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 Line of sight analysis allows us to determine where to put a house or

power plant where it could or could not be seen from major roads. Notice power plant where it could or could not be seen from major roads. Notice the roads actually track up the hills on the right side of the image.the roads actually track up the hills on the right side of the image.

Part II. What can GIS Part II. What can GIS do?do?

Some general types of GIS operations are listed Some general types of GIS operations are listed on the next few slideson the next few slides– Many more are possible than are shown here and more Many more are possible than are shown here and more

are being created every dayare being created every day– Extensions and scripts created by users Extensions and scripts created by users

(http://www.esri.com/arcscripts) (http://www.esri.com/arcscripts) – Third-party and government developers make software Third-party and government developers make software

plug-ins for specific uses (eg. EPAplug-ins for specific uses (eg. EPA’’s BASINS software)s BASINS software)

1. Proximity Analysis1. 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.

2. Query and Overlay 2. Query and Overlay AnalysesAnalyses

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 operation mathematical

operations are done on each pixel of multiple data layers. This results in a new data layer that is calculated from all the input layers.

3. Spatial Analysis3. Spatial Analysis Raster data can also

be used to create surfaces

Other raster data uses: – Density analysis– Proximity analysis– Least-cost paths– Line-of-sight– Hydrology analysis

Part II: Data ExamplesPart II: Data Examples Here is

Atlanta– Highways– Roads– Census

Tracts

Close up of downtown– Map contains data for each

street– Each address in the city can

be geocoded – that is its location estimated in a systematic way

– Length of each street segment - block

– Streets can be sorted by length, name, income, home value, race, age - all provided by the Census Bureau (TIGER)

Atlanta ExampleAtlanta Example Hypothetical population Hypothetical population

of opossums.of opossums.– Data can be sorted by Data can be sorted by

attribute, such as sex, attribute, such as sex, females are females are yellow in yellow in this examplethis example

– Hmmm, why are Hmmm, why are males found closer to males found closer to populated areas?populated areas?

– We do not know – We do not know – but but how else would we how else would we discover the pattern?discover the pattern?

Atlanta Same population now

reclassified by some other 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 the animals are most clustered

– Measure distances between individual locations