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

TLID LENGTH FENAME117843446 0.01467 State Highway 21117843447 0.01425117843448 0.42922 State Highway 21117843449 0.10505117843451 0.31102117843452 0.12941117843453 0.47656117843454 0.54619117843455 0.69272117843468 0.10872 State Highway 21117843472 0.03264 State Highway 21117843478 0.51600117843481 0.01842117843510 0.75529117843511 0.22091 State Highway 21117843512 0.02199117843513 1.32477117843514 0.07625

oF = 9/5 * oC + 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 forInformation Interchange)

• Translates every number and letter into 7-8 digits

• E.g. letter A = 65 (1000001)

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 view Fields view

School

No School

World is empty, except when there is an object

There is information everywhere

Modeling our world: two views

Discreet view Fields 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

(x1,y1) (x2,y2)

(x3,y3)

Polygon (x1,y1)

(x2,y2) (x3,y3)

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

Paper Raster Vector

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 (2.11012, 25.0293)

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

287-4830