Topographic Mapping

Whether on paper or on a computer screen, a map is the best tool available to catalog and view the arrangement of things on the Earth's surface. Maps of various kinds--road maps, political maps, land use maps, maps of the world--serve many different purposes.
One of the most widely used of all maps is the topographic map. The feature that most distinguishes topographic maps from maps of other types is the use of contour lines to portray the shape and elevation of the land. Topographic maps render the three-dimensional ups and downs of the terrain on a two-dimensional surface.
Topographic maps usually portray both natural and manmade features. They show and name works of nature including mountains, valleys, plains, lakes, rivers, and vegetation. They also identify the principal works of man, such as roads, boundaries, transmission lines, and major buildings.
The wide range of information provided by topographic maps make them extremely useful to professional users for engineering, energy exploration, natural resource conservation, environmental management, public works design, along with commercial and residential planning.

Example map

Common Methods and Uses

Aerial Photogrammetry
Aerial Photogrammetry uses aerial photographs to produce planimetric and topographic maps of the earth's surface and of features of the built environment. Effective photogrammetry makes use of ground control by which aerial photographs are carefully compared and registered to the locations and characteristics of features identified in ground-level surveys.

Field Survey Topography
The field survey still plays an important role in making and revising topographic maps. After aerial photographs are obtained, field survey work may be required to establish and measure the map's basic control points and to identify objects that need visual verification.
Survey measurements are taken carefully to establish the control points that become the framework on which map detail is compiled. Two types of control points are needed to position map features accurately. Horizontal control points identify the latitude and longitude of selected features within the area being mapped. They establish correct scale and map orientation and allow accurate positioning of the map's features. Vertical control points determine the elevation of selected points for the correct placement of a topographic map's contours.

LIDAR
LIDAR is the technology of using pulses of laser light striking the surfaces of the earth and measuring the time of pulse return. The LIDAR laser scanner is mounted photogrammetrically in the bottom of an airplane (similar to an aerial camera) along with an Inertial Measuring Unit and Airborne GPS. Robust data storage is required to process the return time for each pulse returned back to the sensor and calculate the variable distances from the sensor, or changes in terrain/land cover surfaces. As with any photogrammetric GPS activity, the LIDAR system requires a surveyed ground-base location to be established in the project area. LIDAR scanning can occur day or night, as long as clear flying conditions are present.