Mapping Then and Now

Mapping Tools in 2006

Global Positioning System Receiver: Used to calculate and record latitude/longitude coordinates and elevation. A GPS can record individual points or a "track" (a line showing the route taken) plus descriptive information at each point. It can also be used as a navigational aid to guide the user to a particular location.

A GPS receiver receives signals from several satellites orbiting at 12,600 miles above earth. These signals include the satellite's location and the exact time the signal was sent. The GPS receiver calculates the time it takes for the signal to travel from satellite to receiver, and from that information calculates the distance between the receiver and satellite (based on the speed of the signal, which is constant). To do this, the GPS receiver must include an extremely accurate clock. In addition, most GPS receivers can determine compass bearings, measure distances, and calculate speed of travel.

Geographic Information System: A combination of computer software, data, and hardware used for creating maps, analyzing information, and storing spatial data. A GIS can be quite elaborate, requiring high-end computers and terabytes of data storage, such as the system used to manage the National Atlas. A GIS also can be small enough to run on a laptop or handheld computer.

GIS software typically includes tools for creating and editing spatial data such as from a database of latitude/longitude coordinates or by tracing aerial photographs or paper maps. It also includes tools for measuring distances and calculating the area and perimeter of features. GIS stores descriptive information about features along with the spatial data. The descriptive data can be used to make "thematic" maps, which show how a phenomenon such as elevation, soil type, or temperature varies from place to place.

Satellite Imagery and Aerial Photographs: Pictures of the earth taken from above show us what exists in different locations. This information is used for navigation, to evaluate the utility of a piece of land for a particular purpose such as farming, and to create maps such as topographic or street maps. Imagery is available in a variety of formats and at many levels of detail from satellite imagery with a resolution of 30 meters to aerial photography with a resolution of six inches.

Theodolite (also called Optical Transit): Used to measure angles, a theodolite consists of a very precise telescope mounted on a tripod with scales for measuring both vertical and horizontal angles. Many theodolites now incorporate electronic controls and laser range finders, making them far easier to use than the earliest versions.