GIS Brownbag Series Part 2: How does GIS model our world?

Chimpanzees?!?

Jane Goodall studies Chimpanzees in Gombe Park in Tanzania

Snapshots of Gombe Park

Satellite image “draped over” an elevation model Yellow dots show Fifi’s feeding spots in 1998

Habitat loss and habitat fragmentation

Representations Model Help us assemble knowledge: you should have an idea of what Gombe Park looks like even though you have never been there (?!) How did we model or represent Gomba Park?

Representations Pictures 3D models Major threat to Chimpanzees: Habitat loss and habitat fragmentation Writing Maps

o F = 9/5 * o C + 32 Other types of representations

You know more about Gomba Park than I have showed you… First law in Geography (by Waldo Tobler) What do you know about this tree? ? What vegetation could you find right here? ?

Tobler’s Law First law in geography: All places are similar, but nearby places are more similar than distant places Is Tobler’s Law always true?

Computers only understand digital information

Computers use standards for interpreting binary code. For example JPEG, TIFF, GIF ASCII ASCII (American Standard Code for Information Interchange) Translates every number and letter into 7-8 digits E.g. letter A = 65 ( )

ASCII Use programming language to manipulate and use ASCII code Examples: C, Visual Basic, Java… ESRI used C++ to program ArcGIS 9

Modeling our world: two views Discreet viewFields view School No School World is empty, except when there is an object There is information everywhere

Modeling our world: two views Discreet viewFields view Shapefiles Coverages Personal geodatabase File geodatabase Rasters Images (.tif,.jpg)

Discreet View Villages modeled as points Roads modeled as lines Park boundaries modeled as polygon Dimension 0D 1D 2D Are villages zero dimensional? Of course not!

Modeling 3D Impossible on a flat screen, but.. Store height as an attribute Referred to as “2.5D” Aerial photograph “draped over” a hillshade

Point (x,y) Line (x 1,y 1 )(x 2,y 2 ) (x 3,y 3 ) Polygon (x 1,y 1 ) (x 2,y 2 )(x 3,y 3 ) Discreet view is modeled with vectors

Key advantages of using vectors 1. You can store information for every object in attribute table Allows for many types of analysis Easy to manipulate data 2. Only need to store data for areas that have a discreet object

Fields view is modeled with rasters

1 cell or pixel Spatial Resolution limited by cell size

Sources of Raster Data: Digital Elevation Models Satellite Imagery Airphotos, Orthophotos Processed airphotos to remove distortions

Compare vectors and rasters PaperRasterVector Info everywhere No info between objects Spatial resolution: scale, e.g. (1:24,000) Cell size Unlimited?: zoom in and out Scale indicated in metadata to indicate accuracy

Accuracy Vs Precision How close is map to reality? How finely can you measure reality? (2, 25) or ( , )

Next Brown Bag Lunch: Where in the world is IDWR? Georeferencing and Projection Thursday August 21 Interested in a specific topic for future lecture? Contact Wilma