User:Mav/Introduction to GIS notes by maveric149/2002-03-05 Lecture

Introduction to GIS notes by maveric149 2002-03-05 Lecture

Location errors:

  • missing polygons
  • distored line
  • dangling arcs
  • unclosed plygons
  • Over shoots and Under shoots - Edited by A.Narayana Murthy.

Topological erros:
false relationships between objects

Spatial data editng
matching linesar features across the border of several maps

  • line simplification
  • line smoothing
  • transfer features between maps

Location errors
superimposition of digital v. hard copy source map

Sources of error
human, scanning and tracing, conversion of coordinates

Topolgical erros

  • violate topological convention (dangling node, from an over/under-shoot of line)
  • Other examples; unclosed polygon


  1. constuct topology
  2. determine tpypes of errors that eist
  3. remove errors and rebuild topology
  4. iterate to find al errors


  • removal of dangle length
  • setting fuzzy tolerance to make digital line snap to the real world one.
if you spicifiy too big a tolerance, then other feature may be affected

needed step antime source data has coverage between two adjacent areas.

  • select on map to be "edit" coverage and the other to be the "snap coverage.

Non-topological editing
delete, omove, cut and paste (whole polygons)

each plgon is unconnected to other one in no0topo GIS
  • reshaping
  • deleting vertex
  • adding vertex
  • split or merge polygons

Other editing funtions

  • line simplification
  • line desification adds points to selected line at specified intervals
  • line smoothing uses math fucintion to modify existing lines