Vector Analysis

Producer Field Guide

HGD_Product
Producer Field Guide
HGD_Portfolio_Suite
Producer

Most of the operations discussed in the previous pages of this chapter focus on raster data. However, in a complete GIS database, both raster and vector layers are present. One of the most common applications involving the combination of raster and vector data is the updating of vector layers using current raster imagery as a backdrop for vector editing. For example, if a vector database is more than one or two years old, then there are probably errors due to changes in the area (new roads, moved roads, new development, and so forth). When displaying existing vector layers over a raster layer, you can dynamically update the vector layer by digitizing new or changed features on the screen.

Vector layers can also be used to indicate an AOI for further processing. Assume you want to run a site suitability model on only areas designated for commercial development in the zoning ordinances. By selecting these zones in a vector polygon layer, you could restrict the model to only those areas in the raster input files.

Vector layers can also be used as inputs to models. Updated or new attributes may also be written to vector layers in models.

Editing Vector Layers

Editable features are polygons (as lines), lines, label points, and nodes. There can be multiple features selected with a mixture of any and all feature types. Editing operations and commands can be performed on multiple or single selections. In addition to the basic editing operations (for example, cut, paste, copy, delete), you can also perform the following operations on the line features in multiple or single selections:

  • spline—smooths or generalizes all currently selected lines using a specified grain tolerance
  • generalize—weeds vertices from selected lines using a specified tolerance
  • split/unsplit—makes two lines from one by adding a node or joins two lines by removing a node
  • densify—adds vertices to selected lines at a tolerance you specify
  • reshape (for single lines only)—move the vertices of a line

Reshaping (adding, deleting, or moving a vertex or node) can be done on a single selected line. The following table details general editing operations and the feature types that support each of those operations.

Add

Delete

Move

Reshape

Points

yes

yes

yes

no

Lines

yes

yes

yes

yes

Polygons

yes

yes

yes

no

Nodes

yes

yes

yes

no

You can undo any edits. The software stores all edits in sequential order, so that each click of Undo reverses each editing step.

For more information on vectors, see Raster and Vector Data Sources.