# GRASS Help System

## WHAT ABOUT SCANNED DATA?

Map data that are scanned electronically are usually scanned as raster data at a very fine resolution (around 100 Microns). The raster data are then converted to GRASS vector file format. When done properly, the degree to which the digital data are different from the original lines is indiscernible. Such files must be checked carefully, however, for errors introduced because of mislabeled polygons, unsnapped nodes or some misunderstanding on the part of the persons doing the scanning as to what exactly was required.

Once made digital, vector data must be run through the GRASS program v.to.rast in order to be converted to raster format. Any vector to raster conversion will result in the zigzag lines characteristic of raster data.

See the sections entitled "Raster, Vector, and Sites Data File Formats" and "Resolution" under the Main Menu selection, "Setting Up a GRASS Database".

Also: "Cartographic Issues in the Development of a Digital GRASS Database",

a USACERL Special Report N-09/16 (Marilyn Ruiz and Jean Messersmith,
Sept/1990), from which this information was taken.

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Automatically created on: Sun Mar 5 12:05:43 2006