# GRASS Help System

## PREPARING A MAP FOR DIGITIZING

A great amount of information is stored on paper maps. This information can be much more easily manipulated in a computer database. To get map data into a GRASS database, map data (analog data) can be converted into digital data by tracing relevant map features using a digitizer. The digitizer converts map data into a GRASS vector format.

Frequently, map data cannot readily be digitized directly from original paper source maps. Paper maps will generally contain many types of information. The person that is digitizing must know exactly what information is to be digitized. It is therefore generally necessary for the user to prepare a map(s) containing only the information that is to be digitized before beginning to digitize.

Have the following items before beginning to digitize:

- a stable medium, i.e., mylar, plastic, etc. on which the features
to be digitized appear clearly and accurately

- at least 10 marked points on the medium corresponding to database
(e.g., UTM) coordinates

- a region in database coordinates defining the area being digitized

- a region in database coordinates defining the area of the resultant
raster data file

- a map of the area being digitized near the digitizer readily
available for reference

- masking or drafting tape to secure the medium

- a planned final region and resolution for the raster data file.

"Cartographic Issues in the Development of a Digital GRASS Database" (Ruiz and Messersmith, 1991) describes how maps should be prepared for digitizing; it should be read prior to digitizing.

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Automatically created on: Mon Mar 6 12:34:40 2006