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Geography 241 – GIS IDr. Patrick McHaffieAssociate ProfessorDepartment of Geography
Cook County, % population < 5
What is a GIS?
Geographic Information System - collection, organization, maintenance, analysis, and output of spatially-referenced information.
Two important components - What, and Where
We usually understand GIS to be computer-facilitated system
GIS is NOT only software/hardware
Also includes:
•Trained personnel
•Supporting Institution
•Protocols for use
GIS HardwareTypical of most computer systems, with a little more storage, a few added tools for input/output.
Coordinate input devices are the primary “specialized” hardware.
Digitizing Tablets GPS receivers.
INPUT ANALYSISSTORAGE
OUTPUT
DigitizingGraphic editing,error correction: sliver removal, data sanitation, Tabular data entry and editing Data reductionText conversion
Graphic analysis capabilities -topology creation,reclassification, buffer, overlay, network, neighborhood functions, coordinate managementDatabase managerStatistical functions
Map compositionColor palette generationSymbol generation, editingGraphic overlayScreen queryGeographic query
GIS Software
What is in it for me?
Take a sheet of paper, put your name and major at the top. Then,
In a five minute free write, answer the question:
How can you imagine you might be using GIS and other Geotechnology in 5 years?
1.2 , 4 .75 .8 , 3 .68 .9 , 7 .2..
Real W or ldDat a M odel Dat a
S t r uct ur e
phenomena that exist
An abstraction, relevant phenomena and properties
computer representation
REPRESENTATION AND DATA
STRUCTURES
•Most common data models define thematic layers
•Typically, layers, one layer for each distinct view of a theme
PointsPoint ID X Y 1 32.7 45.6 2 76.3 19.5 3 22.7 15.8etc…..
1 2
3 4
Organization
Lines6
9
1
239
AB
C Line Begin End ID Point Point A 6 9 B 9 1 C 239 1etc…..
Polygons
13
22
41954
11
12
52
53
PolygonID Lines
A 11, 12, 52, 53, 54
B 52, 53, 9, 41, 22, 13
Three Types of Vector Features
Vector TopologyTopology – geometric properties that to not change with shape: Adjacency, connectivity, containment
Raster – The Mixed Pixel Problem
Landcover map –Two classes, land or water
Cell A is straightforward
What category to assignFor B, C, or D?