Getting the Map Getting the Map into the Computerinto the Computer

Getting Started with

Geographic Information Systems

Chapter 4

Data requirements and Data requirements and sourcessources

Most economic uses of geographic data require:

cartographic data publicly available demographic and

economic data privately available data proprietary data

GIS cartographic data can beGIS cartographic data can be

Purchased. Found from existing sources in digital form. Captured from analog maps by

GEOCODING.

GIS attribute data can beGIS attribute data can be

Purchased Found digitally or on maps Proprietary, in digital or non-spatial form

GEOCODING ADDRESS MATCHING

Address matchingAddress matching

Much customer, vendor, or facilities data are available by street address, or at least ZIP Code.

The spatial data handling functions of most GISs can assist with address matching into a spatial database, given required data.

There are always problems.

Commercial vendorsCommercial vendors

Finding Existing Map DataFinding Existing Map Data

Map libraries Reference books State and local agencies Federal agencies Commercial data suppliers

Federal Data AgenciesFederal Data Agencies

USGS NOAA Census Bureau many more...

National Spatial Data ClearinghouseNational Spatial Data Clearinghouse

U.S. Bureau of the CensusU.S. Bureau of the Census

Your Spatial Data “Rights”Your Spatial Data “Rights” US Federal

FOIA COFUR

State Local Protection for national security, proprietary

info, privacy Attributes vs. map data

GEOCODINGGEOCODING

Geocoding is the conversion of spatial information into digital form.

Geocoding involves capturing the map, and sometimes also capturing the attributes.

Geocoding methods for mapsGeocoding methods for maps

Digitizing Scanning Field Data Collection

GEOCODING LEAVES A GEOCODING LEAVES A “STAMP” ON DATA“STAMP” ON DATA

The method of geocoding can influence the structure and error associated with the spatial information which results.

Example: scanning (raster), digitizing (vector).

DigitizingDigitizing

Captures map data by tracing lines from a map by hand

Uses a cursor and an electronically-sensitive tablet

Result is a string of points with (x, y) values

The Digitizing TabletThe Digitizing Tablet

Digitizer cursor transmitsa pulse from an electomagneticcoil under the view lens.

Pulse is picked up bynearest grid wires undertablet surface.

Result is sent tocomputer afterconversion tox and y units.

map

Selecting points to digitizeSelecting points to digitize

Scanning Scanning

Places a map on a glass plate, and passes a light beam over it

Measures the reflected light intensity Result is a grid of pixels Image size and resolution are important Features can “drop out”

Field data collectionField data collection

The Role of ErrorThe Role of Error

Enforcement for map data is usually by using topology.

Map and attribute data errors are the data producer's responsibility, but the GIS user must understand error.

Accuracy and precision of map and attribute data in a GIS affect all other operations, especially when maps are compared across scales.

Geocoding other recordsGeocoding other records

A common operation Based on some geographic attribute of

records that our software can relate to geographic coordinates: street address (TIGER or private match data) ZIP codes or Census tracts (allocate to

centroids)

coming next…..coming next…..

What is where?