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Government 90dnMapping the Census

Lecture 3: More on GIS; Spatial Data

Structures;TIGER

Sumeeta Srinivasan

ssrinivasan@cga.harvard.edu

Reference: Unlocking the Census, Ch 2; TIGER documentation www.census.gov;

Introduction to GIS (Huxhold); Geographic Information Systems and Science,Longley, Goodchild, et al.

mailto:ssrinivasan@cga.harvard.eduhttp://www.census.gov/http://www.census.gov/mailto:ssrinivasan@cga.harvard.edu

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Outline

What is GIS?GIS Data types

Raster vs Vector

Data structures

TIGER data structure for address matching

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Geographic InformationMultidimensional

Has volume

Requires projection to flat surface

Analyses require data integrationUnique analysis methods

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Geographic Information System

(Definitions)

Container of mapsComputerized tools for solving geographic

problems

Mechanized inventory of geographically

distributed features and facilities

Method for revealing patterns andprocesses in geographic information

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Geographic Information System

Container of maps

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Geographic Information System

Mechanized inventory of geographicallydistributed features and facilities

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Geographic Information System

Computerized tools for solving geographicproblems

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dotdgis.dotd.louisiana.gov

dotdgis.dotd.louisiana.gov/website/GIS-T2006.ppt

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Geographic Information System

Method for revealing patterns andprocesses in geographic information

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Spills in Boston, Cambridge, Somerville

Hazardous

and Oil Spills

Center

(close to intersection

of Main and Portland

in Cambridge)

Directional

Ellipse forSpills

Mean

Population

WeightedCenter

(close to

intersection of

Fenway andForsyth in Boston)

Directional

Ellipse for

Population

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Geographic Information System

(Definitions)

Container of mapsComputerized tools for solving geographic

problems

Mechanized inventory of geographically

distributed features and facilities

Method for revealing patterns andprocesses in geographic information

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GIS Data Models

Discretize Geographical Realityfield view (regions) vs. object view (objects in aplane)

Data Model implies spatial sampling andspatial errors

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Rasters and Vectors

How to digitally represent phenomenaconceived as fields or discrete objects?

Field View: Raster

Object View: Vector

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Real World

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Raster vs VectorData Structure

0 1 2 3 4 5 6 7 8 9

0 R T

1 R T

2 H R

3 R

4 R R

5 R

6 R T T H

7 R T T

8 R

9 R

Raster Representation

line

polygon

point

Vector Representation

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Lab Exercise 2

Step by step creation of data structuresPoint, line and polygon tables

Topology tables

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Topology in Data StructuresDefined as the spatial relationships between

neighboring featuresImplemented within data structure by defining:

connectivity: Which arcs meet at a node?

area definition: Which arcs make up the

polygon?

contiguity: Which polygons are on the left andright?

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Lab Exercise 1

How to use TIGER data to match up Tuscaloosaschool addresses?

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TIGER FilesLinesstreets, railroads, rivers

Areaszip codes, census blocks, tracts, places, counties, etc.

Pointslandmarks such as churches, schools, and other cultural

features represented in TIGER as points

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Linear Address Matching (Streets)Urban street maps

Four street address numbers ranging from low to high for

each side of a street segment.

Left_from Left_to Right_from Right_to Street_name Type

101 199 100 198 OAK ST

0105

0107

100 198

101 199

Oak St.

(80.731, 40.025) (80.729, 40.025)

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Address Matching Major Steps

1437

402

855

123 Oak St

333 Pine Av

18 Bay Dr

A

A

B

ID Address Class

Schools file

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Address Matching Major Steps1437

402

855

123 Oak St

333 Pine Av

18 Bay Dr

A

A

B

ID Address Class

Schools

98

99

198

199

Oak

Oak

Oak

Oak

R

L

R

L

O

E

E

O

To Street Side ParityFrom

1

100

101

2

Type

St

St

St

St

Attributes of Streets

Street_

5950

5950

6011

6011

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Address Matching Major Steps1437

402

855

123 Oak St

333 Pine Av

18 Bay Dr

A

A

B

StoreID Address Class

schools

98

99

198

199

Oak

Oak

Oak

Oak

R

L

R

L

O

E

E

O

To Street Side ParityFrom

1

100

101

2

Type

St

St

St

St

Attributes of Streets

Street_

5950

5950

6011

6011

5950 6011Oak St

PineAv

100

101

198

199123

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Converting GeoreferencesGIS applications often require transforming

data so that they line upThese are standard functions in popular GIS

packages

Street addresses must be converted to

coordinates for mapping and analysis

Usinggeocoding functions