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

Coordinates and Attributes

Many objects for a theme, with properties recorded for each object

REPRESENTATION AND DATA

STRUCTURES

•Most common data models define thematic layers

•Typically, layers, one layer for each distinct view of a theme

Cartesian Coordinates

Point s

L ineA r ea

Vect or Rast er

Point s

L ineA r ea

( x ,y )

X

Y

Common Data Models

Vectors Define Discrete Features

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

Rasters – Fixed Cell Size, Grid Orientation

Rasters – Discrete or Continuous Features

discrete continuous

Raster – The Mixed Pixel Problem

Landcover map –Two classes, land or water

Cell A is straightforward

What category to assignFor B, C, or D?

Summary

• GIS are systems for the creation, maintenance, analysis, and conveyance of spatial data

• We represent abstractions of our world into spatial and attribute components using data models and data structures

• Two major data models – raster and vector