2. Digitizing
There are three primary methods for digitizing spatial information:
Manual Methods include:
Tablet Digitizing
Heads-up Digitizing
An Automated Method includes:
Scanning and Vectorization

4. Manual Digitizing
Ref: Getting Started with GIS, by K. Clarke

5. How is it done?
Although methods vary, the typical steps for digitizing a paper map require the following:
Physical Preparation
Digitizer Set up
Map preparation
Digital Preparation
Map registration
Digital Collection
Feature collection
Feature correction
Save, save, save

6. Creating New Data (Cont’d)
Manual Digitizing:
Digitizing tables used (tedious process)
Electronic mesh senses cursor position
Paper maps (e.g. Topo Maps) are sources of most GIS themes that we use
Point or stream mode digitizing done
Now-a-days mainly done in 3rd world
Need to record ref. coor. converted to real-world coor. (GIS coverage)
Digitizing polygons need labels (ID)
Careful planning needed before you digitize

7. Heads up Digitizing
Digitizing and scanning

8. Scanning
Ref: Getting Started with GIS, by K. Clarke

9. Creating New Data (Cont’d)
Scanning:
Scan a map into binary grid file
Can be converted back to vector thru tracing (i.e. line thinning extracting topo-reconstruction or smoothing)
Software available to clean scanned images
Resolution is an issue (e.g. a line = 5-6 pixels)
Digital maps are as good as the source map

10. Creating New Data (Cont’d)
On-Screen (head-up) Digitizing:
Relatively easy to do
Good for updating/editing changes
You can add points, lines, polygons
You don’t have to register points as in manual digitizing
Geometric Transformation:
Digitized maps have same coor. As source map
You may have to convert to real-world coor. & projection using control points.

11. Raster to Vector Conversion
Able Software R2V
AutoDesk Raster Design
ESRI ArcScan

13. Filters

16. Rubber Sheeting: Spatial database editing software that attempts to correct errors by stretching a map to fit known control points or monuments.

18. Why Topology Matters
Topology allows automated error detection and elimination
Need to build/clean topology for digitized/scanned maps
Unconnected nodes are snapped
Slivers from digitizing are eliminated
Topology makes map overlay feasible
GIS operations are done w/o accessing the point files

19. Overshoots and undershoots
Why do I want Topology?
Gaps and slivers
Overshoots and undershoots

20. Non-Topology
Ref: Introduction to GIS by K. Chang

21. Creating New Data
Remotely sensed data
Georef; 1m x 1m resolution; good as a background map for other themes
Ref: Getting Started with GIS, by K. Clarke

22. Creating New Data (Cont’d)
GPS: differential GPS have cm-scale resolution
Measures ranges (distances of receivers by 24 NAVSTAR satellites using radio signals & atomic clocks)
Ref. or base stations can reduce noise
Diff. GPS comes w/ software to download data
Hand-held GPS data can be downloaded too
Ref: Getting Started with GIS, by K. Clarke

23. Creating New Data (Cont’d)
Field Survey Data:
defines parcels by azimuth & distances
Uses Total Station, Stadia, Laser Ranging, and COGO software
Ref: Getting Started with GIS, by K. Clarke

24. Methods of Collecting Data
Existing data, downloads from field
Keyboard
COGO

25. Creating New Data (Cont’d)
Street Addresses:
Point features, street segment length, even/odd house numbers with side descriptions (e.g. TIGER files) can be geocoded
TEXT Files: lat/long in dec. degrees cane converted to an event theme
Ref: Getting Started with GIS, by K. Clarke

26. Geocoding

27. What is Conflation?
the process of transferring attributes from a source line layer based on one level of accuracy and precision to a target line layer of a different precision and accuracy.

28. Format & Exchanging of GIS Data
Can import different data formats or use utility programs (e.g Import 71) to convert data
GIS accept TIF, GIF, JPEG, AutoCAD data formats (needs right extensions) which are not georeferenced
Vector to Raster conversion is easy, opposite is hard
Data exchange by import/export involves errors in attributes & geometry
ESRI New Product called Data Interoperability
Efficient data transfer is important for the future of GIS
OpenGIS® Specifications on
GML Geographic Markup Language
WMS Web Map Service
WFS Web Feature Service