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The third reason for editing is to make a map more legible. A conventional
map, as well as a display on the screen, is a communication medium that
graphically conveys to users geographic information. Because of the
limited space provided by a map and the large amount of information that
is normally shown on it, cartographers use various techniques to enhance
the graphic message for easier reading. Cartographic enhancements address
the following issues:
Name placement - Text annotations are added to the map to depict some of
the feature attributes. For example, we add text to show the names of
roads, rivers, buildings, and so on. Names for linear and area features
are often curved, and names in dense areas of the map have to be arranged
so as to avoid clustering. Contour labels follow special cartographic
rules to ensure that they can be read without rotating the map. Generalization - This is a technique of making use of the limited space available on the map to effectively depict geographic information. At a small scale, features that are too thin or small to be visible have to be exaggerated in size. This expansion could interfere with the surrounding features, and the affected features have to be moved to maintain topological consistency. Symbolization - Annotation text alone is not enough to represent all the
attributes of features. In fact, too many annotations could create
clustering. A very effective way of visually representing the attributes
is to symbolize the point, line, and area features. For instance, a dashed
line can be used to indicate that a highway is under construction, and a
double line can be used to indicate that the highway has multiple lanes. Graticule - A network of grids on a map labeled with coordinates form a graticule, which helps the reading of positions. A map is not just a visual depiction of the geographic features, it is also a database. In order to facilitate geographic feature retrieval and spatial analysis, maps are superimposed with a graticule labeled with coordinates. This allows reading of the coordinates of any point on the map, and when given the coordinates of a feature, the graticule helps the quick location of it on the map. These coordinates can then be used to compute distance, area, angle, and other measurements. Margin information - Supplementary information about the map, such as its scale, map projection, reference ellipsoid, map identification number, and year of the survey are placed around the margin of the map.
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