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

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

Errors
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

Process

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

Examples

• 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

Edgematching
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