Chapter 5: Spatial Data Editing

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Chapter 5Spatial Data Editing

• Paul Sutton
• psutton_at_du.edu
• Department of Geography
• University of Denver

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Spatial Data Editing

• Definition The removal of errors from updating
  of digital maps
• Newly created digital maps always have errors
• Fixing a new map virtually identical to updating
  an old one

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Two kinds of Spatial Data Errors

• Type 1 Location Errors
• Missing Points, Lines, or Polygons
• Points, Lines, or Polygons in wrong place
• Extra Points, Lines or Polygons
• Type II Logical or Topological Errors
• Overshoots and Undershoots
• Multiple Nodes Etc.

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Non-Error Spatial Data Editing

• Edge Matching
• Line Simplification
• Line Densification
• Line Smoothing
• Cutting Pasting Data from one place to another

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Outline

• Define Location Topological Errors
• Contrast Topological Error with Non-Topological
• Global Local Topological Editing
• Edgematching
• Non-Topological Editing
• Feature Manipulation

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Location Errors

• Location Errors often Identified with a Check
  plot or Check Map
• Aerial Photo or Satellite Image often used as a
  background check of vector data
• On a 124,000 map .1 Inch 20 feet
• Sources of Error
• Human - Scanning Tracing - Digital Conversion

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Topological Errors

• Overshoot Undershoot
• Dangling Arcs
• Sliver Polygons
• Dangling Nodes
• Pseudo-Nodes
• Unclosed Polygons
• Multiply Labled Polygons

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Overshoots Undershoots
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Dangling Nodes
In some cases, a dangling node may be acceptable
for example, in a street centerline map,
cul-de-sacs are often represented by dangling
nodes.
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Dangling Nodes IIThe Unclosed Polygon
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Pseudo-Nodes
Pseudo nodes do not necessarily indicate an
error or a problem. Acceptable pseudo nodes
may represent an island or the point where
attribute values change along a linear feature
(e.g, road type changes from pavement to
gravel).
Pseudo nodes drawn with a diamond symbol occur
where a single line connects with itself (an
island) or where only two arcs intersect. This
might indicate that a connection to another arc
was missed, or that a node was inadvertently
inserted.
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Basics of an Arc/INFO coverage
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Sliver Polygons
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F-Node T-Node Error
The From node To Node In a hydrological
coverage Needs to be correct for Hydro Modeling.
How do you think it Works?
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Multiple Poly Labels
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Topological vs. Non-Topological

• Topological Data can be Cleaned and Built
  automatically w/ Arc/INFO, AutoCAD, MGE, and
  SPANS
• ArcView MapINFO are Non-Topological
• Trend is away from Topological Data

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Topological Editing

• Global Clean and Build Command used Dangle
  and Fuzzy tolerances to fix the topology of a
  whole vector coverage at once.
• The Clean command removes overshoots, connects
  undershoots, and snaps multi-nodes into one node.
• The Build command re-creates all tables with
• F-node, T-node, R-Poly, L-Poly attributes but
  
• Does not create new nodes by snapping or
  intersecting arcs

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The Clean function
CLEAN builds polygon and arc-node topology by
performing a geometric analysis on the coverage
arcs and label points to identify coverage nodes
and polygons. CLEAN finds intersections
between arcs, splits the arcs and codes the
intersections as nodes (i.e., arc endpoints).
During CLEAN, two or more arc coordinates within
the fuzzy tolerance of each other are snapped
together (i.e., become the same coordinate
point). No distinction is made between interior
arc coordinates and nodes or between arcs.
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The Build Function

• The BUILD command performs similar processing
  operations. BUILD with the POLY option creates
  polygon topology and attributes (i.e., a PAT).
  BUILD with LINE will create an AAT or rebuild one
  if it exists. BUILD does not, however, perform
  coordinate editing as does CLEAN. For example, it
  cannot split arcs where they intersect with other
  arcs.

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The Dangle Parameter
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The Fuzzy Tolerance Parameter
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Local Topological Editing

• Lots of zooming in and out Panning
• Lots of setting Nodesnap and Editdistance
  parameters
• Lots of undo aka oops
• Involved work done in prisons.

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EdgematchingMerge Command in Arc/INFO, All
editing problems are back for issues between
coverages rather than within coverages
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Non-Topological Editing(Demonstration at end of
lecture)

• Note Shapefiles are Non-Topological
• Planar Enforcement is gone
• Deleting a polygon creates a void space
• Common Functions Other Functions
• Delete - Reshape
• Move - Split
• Cut - Merge
• Paste

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Common Shapefile Edit Options
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Line Simplification(decreases data storage needs)
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Line Smoothing(increases data storage needs)
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Line Densification
Important when re-projecting. Box Example from
Geographic to Conic
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Concluding Demonstration

• Non-Topological Spatial Data Editing using
  ArcViewFrom the CD exercises for the Chang Text