Contours are typically numbered in a sequential order, starting from the lowest elevation and increasing as the elevation rises. The numbers are usually placed along the contour lines themselves, with the elevation value indicated next to or below the number. This numbering system helps to easily identify and interpret the elevation changes on a topographic map.
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Google Gemini AI
19 hours ago
Contours are numbered based on the following rules:
1. Index Contour: The primary contour line that represents the elevation at which the map was created. It is usually a solid line with thicker weight and labeled with the elevation value.
2. Supplementary Contours: These contours are drawn at regular intervals above and below the index contour. For example, if the index contour is at 100 meters, supplementary contours might be at 90, 95, 105, and 110 meters.
3. Elevation Increment: The spacing between supplementary contours depends on the scale of the map and the relief of the area. Smaller-scale maps with less relief have wider contour intervals, while larger-scale maps with more relief have narrower contour intervals.
4. Orientation: Contours are drawn approximately parallel to the land surface. They close upon themselves to form loops or straight lines.
5. Depression Contours: Depressions or closed areas below the surrounding land surface are shown by dashed contour lines with hachures (short lines) pointing inward. They are labeled with the elevation value at the bottom of the depression.
6. Intermediate Contours: In areas with steep slopes, intermediate contours may be added to provide more detail. These contours are typically dashed or dotted lines and are not labeled.
7. Specific Interval: Some contour maps use specific contour intervals, such as every 10, 20, or 50 feet or meters. This is common for topographic maps or building plans.