Getting the Map into the Computer

1
Getting the Map into the Computer

• Getting Started with
• Geographic Information Systems
• Chapter 4

2
Data requirements and sources

• Most economic uses of geographic data require
• cartographic data
• publicly available demographic and economic data
• privately available data
• proprietary data

3
GIS cartographic data can be

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

4
GIS attribute data can be

• Purchased
• Found digitally or on maps
• Proprietary, in digital or non-spatial form
• GEOCODING
• ADDRESS MATCHING

5
Address 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.

6
Commercial vendors
7
Finding Existing Map Data

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

8
Federal Data Agencies

• USGS
• NOAA
• Census Bureau
• many more...

9
National Spatial Data Clearinghouse
10
U.S. Bureau of the Census
11
Your Spatial Data Rights

• US Federal
• FOIA
• COFUR
• State
• Local
• Protection for national security, proprietary
  info, privacy
• Attributes vs. map data

12
GEOCODING

• Geocoding is the conversion of spatial
  information into digital form.
• Geocoding involves capturing the map, and
  sometimes also capturing the attributes.

13
Geocoding methods for maps

• Digitizing
• Scanning
• Field Data Collection

14
GEOCODING LEAVES A 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).

15
Digitizing

• 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

16
The Digitizing Tablet
17
Selecting points to digitize
18
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

19
Field data collection
20
The 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.

21
Geocoding 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)

22
coming next..

• What is where?