This document discusses types of errors that can occur during spatial data editing and digitizing, including location errors, mechanical errors, human errors, and topological errors. It describes tools and processes for correcting errors such as CLEAN, nodesnap, editdistance, EXTEND, SPLIT, and edgematching. Both topological and non-topological editing approaches are covered.

1. Spatial Data Editing
Chapter 5

2. Introduction
 All digitizing involves errors
 In the real world, revisions are required
 Keeping data up-to-date is part of the job
 Types of errors
• location
• mechanical
 In order to edit, must know the structure
 Accuracy and metadata

3. Type of Digitizing Errors
 Location errors – by source, by human hand,
or machine: not at correct location
 Check plot at same scale to visually note
errors
 Standard for accuracy by Natural Resources
Conservation Service says 0.01 inch line width
of map.
 At 1:24,000 represents 20 feet on ground (6-7
meters)

4. Type of Digitizing Errors
 Human errors
 Scanning, tracing, follow wrong line
 Conversion or transformation errors
(generally show in a pattern)
 Duplicate lines
 Slivers (tiny polygons) created

5. Topological Errors
 Arcs not meeting
• undershoot and overshoot
 Result is dangling arc/node
 Same if a polygon is not closed.
 Symbol is □ square.
 Dangling nodes can be acceptable
(small streams, dead end streets)
 Pseudo node, symbol is ◊ diamond

6. Topological Errors
 Pseudo node when not at line end or
intersection
 Symbol is ◊ diamond
 May be acceptable to show changes in
attribute date, or start of isolated polygon.
 Direction of arc by from-node and to-node.
 Can be reversed by ARC/INFO

7. Topological Errors
 Polygon is linked to attribute data by
label point.
 Symbol is + plus sign
 Multiple label points are not acceptable
and indicate an error

8. Topological and
Non-topological Editing
 Each vendor has system
 Topological have means for visualizing
and correcting errors
 Some non-topological vendors provide
assistance in spatial relationships
 Non-topological can digitize and edit, but
cannot build topology

9. Topological Editing
 Steps
• Construct topology
• Note errors visually
• Correct errors
• Rebuild topology
 Normally an iterative process

10. Correcting Digitizing Errors
 Global or local
 Global uses tolerances for CLEAN
• dangle length
• fuzzy tolerance
 CLEAN removes overshoot and undershoots if
less then the dangle length
 CLEAN inserts nodes and enforces arc-node
relationship

11. Correcting Digitizing Errors
 CLEAN removes vertices less than fuzzy
tolerance
 CLEAN can remove undershoots if the
dangle length is too large
 CLEAN can snap node if too large
 Any action by CLEAN (or BUILD) can
reduce the accuracy of the map

12. Correcting Digitizing Errors
 Local tolerances
• nodesnap
• editdistance
 Must be “just right”
 Snapping moves and distorts arc
 Set by value or by interactive
 Zoom in

13. Correcting Digitizing Errors
 Tools for local editing
• UNDO or OOPS can reverse, one action at a time
• EXTEND an arc for undershoot
• SPLIT an arc inserts a node
• Select and delete overshoot
• Select and delete duplicate arcs, but which?
• FLIP to change arc direction
• UNSPLIT to remove pseudo nodes
• Add label points or close polygon
• VERTEX command to reshape line

14. Edgematching
 Quad to quad transition
 Edgematch to join together
 Usually requires zoom
 Interactive process to “connect”
components
 Use DISSOLVE to remove the boundry

15. Non-topological editing
 Can be “heads-up”
 Easier to use because can
• delete
• move
• cut
• paste
 Reshape lines and polygons by drag and
drop of vertices

16. Non-topological editing
 Vertex edit can add new vertices
 Split and merge
 Can create variations not possible in
topological data
• overlapping
• doughnut

17. Other types of map feature
manipulation
 Line simplification
• Douglas-Peucker algorithm
 Line Densification
• why?
 Line smoothing
• mathematical
• SPLINE
 Transfer (and copy) of features
• GET and PUT