General requirements for topographic maps

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GENERAL REQUIREMENTS FOR TOPOGRAPHIC MAPS

The scale and contour interval of a map that you are preparing will be specified according to the purpose for which the map will be used. Obviously, a map that will be used for rough design planning of a rural dirt road will be on a smaller scale and have a larger contour interval than one to be used by builders to erect a structure on a small tract in a built-up area.

The extent to which details must be shown may also be specified; if not, it is usually inferred from the purpose of the map. The following guidelines suggest the nature of typical map specifications.

A map should present legibly, clearly, and concisely a summation of all information needed for the use intended, such as planning, design, construction, or record.

Topographic maps for preliminary site planning should preferably have a scale of 1 inch = 200 feet and a contour interval of 5 feet. These maps should show all topographic features and structures with particular attention given to boundary lines, highways, railroads, power lines, graveyards, large buildings or groups of buildings, shorelines, docking facilities, large rock strata, marshlands, and wooded areas. Secondary roads, small isolated buildings, small streams, and similar minor features are generally of less importance.

Topographic maps for detailed design for construction drawings should show all physical features, both natural and artificial, including underground structures. Scales commonly used are 1 inch= 20 feet, 1 inch= 40 feet, and 1 inch = 50 feet. The customary contour interval is 1 foot or 2 feet, depending on the character and extent of the project and the nature of the terrain. Besides contour lines, show any spot elevations required to indicate surface relief.

Additional detail features that are usually required include the following:

1. Plane coordinates for grid systems, grid lines, and identification of the particular system or systems.

2. Directional orientation, usually indicated by the north arrow.

3. Survey control with ties to the grid system, if there is one. This means that the principal instrument stations from which details were located should be indicated in a suitable manner.

4. All property, boundary, or right-of-way lines with identification.

5. Roads and parking areas, including center-line location and elevation, curbs, gutters, and width and type of pavement.

6. Airport runways, taxiways, and apron pavements, including center-line locations with profile elevations and width and type of pavement.

7. Sidewalks and other walkways with widths and elevations.

8. Railroads, including center-line location, top-of-rail elevations, and any turnouts or crossovers.

9. Utilities and drainage facilities, such as gas, power, telephone, water, sanitary sewer and storm sewer lines, including locations of all valve boxes, meter boxes, handholes, manholes, and the invert elevations of sewers and appurtenances.

10. Locations, dimensions, and finished floor (usually first floor) elevations of all structures.