intro to cartography

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CARTOGRAPHICSYMBOLOGY.docx

CARTOGRAPHIC SYMBOLOGY

Mapping data, a feature on a map, is split into three types: polygon, line (or arc) and point data.

Polygons are used to represent areas such as the boundary of a city (on a large scale map), lake, or forest.  Polygon features are two dimensional and therefore can be used to measure the area and perimeter of a geographic feature. Polygon features are most commonly distinguished using either a thematic mapping symbology (color schemes), patterns, or in the case of numeric gradation, a color gradation scheme could be used.

In this view of a polygon based dataset, frequency of fire in an area is depicted showing a graduate color symbology.

In this view of a polygon based dataset, frequency of fire in an area is depicted showing a graduate color symbology.

Line (or arc) data is used to represent linear features. Common examples would be rivers, trails, and streets.  Line features only have one dimension and therefore can only be used to measure length.  Line features have a starting and ending point. Common examples would be road centerlines and hydrology. Symbology most commonly used to distinguish arc features from one another are line types (solid lines versus dashed lines) and combinations using colors and line thicknesses. In the example below roads are distinguished from the stream network by designating the roads as a solid black line and the hydrology a dashed blue line.

Streams are shown as dashed blue lines and roads as solid black lines in this example.

Streams are shown as dashed blue lines and roads as solid black lines in this example.

 

Point data is most commonly used to represent nonadjacent features and to represent discrete data points. Points have zero dimensions, therefore you can measure neither length nor area with this dataset. Examples would be schools, points of interest, and in the example below, bridge and culvert locations.  Point features are also used to represent abstract points. For instance, point locations could represent city locations or place names.

GIS point data showing the location of bridges and culverts.

GIS point data showing the location of bridges and culverts.

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