CHAPTER 13:  DIGITAL MAPS

13.1  INTRODUCTION

Maps serve a dual purpose for military use:  for navigation and for tactical displays.

 Maps have traditionally been made from paper for navigation.  Early digital maps

could only show a subset of the data available on paper maps, such as roads.  The

maps and display units could not provide topographical, thematic or other

information.  Today, digital maps for navigation and tactical displays have been

developed showing all the map information, that only paper maps could show

previously.  This chapter discusses digital maps and tactical displays, particularly

with their relevance to GPS.  Modern digital mapping and/or geographic information

systems can easily relate data if the data has been geographically coded.  Tools

can be provided to locate all data points of a particular type within a particular

region, calculate areas, distances, etc.  ZOOM and SCROLL features can be used

to more closely examine areas of interest, or eliminate extraneous information. 

Different types of data can be allocated to a unique layer, which can then be added

or removed from the display as desired.  Additional tools can be provided which

make it easy to convert distances  and measurement units from one format to

another. 

13.2  WHAT IS A DIGITAL MAP?

There are basically three types of digital maps today:

a. "Digitized" paper maps

b.  Digital database maps

c.  Hybrids

These maps are distributed in a variety of logical and physical formats.  Physical

formats include cartridges, CD ROM, tape, and floppy disk.  Logical data formats

vary depending on the manufacturer.  When selecting a digital map, be certain that

the format is compatible with the software product that will be using the data.

13.2.1  Digitized Paper Maps

Digitized paper maps are not digital maps in the true sense.  The digitized paper

map is made by using an optical reader to "read" the infor mation from a paper map,

digitize it and store it in a database and then project the digitized paper map

information on a video screen.   There are two basic methods for storage of digitized

paper map information:  it can either be stored as vector informa tion, or as raster

information.  The vector method is to define every point of a contour that shall be

displayed on the map as a point on the end of a vector.  Each vector will originate

from a selected point on a map.  The com puter will "fill in" the open areas inside the

contours with different colors depending on whether the contours are land masses,

a navigation buoy, etc.  This method requires the least data storage.  In the raster

storage method, an optional scanner scans the map and stores every bit of

information from the paper map, including the "fill in" for contours.  This method

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