Where Am I

The map shows a 25 x 25 mile square of San Diego, California. The vehical icons overlayed on the map represent a trip from Poway to San Diego, California, a distance of approximately 18 miles. The icons represents a location at a specific point in time. The route begins in Poway (upper right) and shows tracks along Ted Williams parkway (Route 56). The trip continues down highway I15 and finally along Mira Mesa Blvd which runs east and west. The black area on the left is the Pacific Ocean. This image was created using APRS. The software consists of WinAPRS on the receiving side and a D700 Kenwood APRS tracker on the transmitting side. Although not obvious, there are actually two map images superimposed over each other. One is a surface contour map of the earth (see description of DEM files below) and the other is a map showing streets, highways, and rivers.

DEM files, or Digital Elevation Model files are produced by the USGS. These files are available for all of the U.S. A Digital Elevation Model (DEM), consists of a sampled array of elevations for ground positions that are normally at regularly spaced intervals. The 1-Degree DEM (3- by 3-arc-second data spacing) provides coverage in 1- by 1-degree blocks for all of the contiguous United States, Hawaii, and limited portions of Alaska. The basic elevation model is produced by or for the Defense Mapping Agency (DMA), but is distributed by the USGS, EROS Data Center, in the DEM data record format. In reformatting the product the USGS does not change the basic elevation information. 1-degree DEM's are also referred to as "3-arc second" or "1:250,000 scale" DEM data. These DEM files can be downloaded

The "tracks" on the map were layed using the vehicle shown. Located in the center of the trunk is a GPS unit (yellow). Also shown is a vertical whip antenna which is used to broadcast APRS packets from a transmitter located within the vehicle. The radio beacons contain latitude and longitude information which are broadcast at intervals (typically 1-2 minutes) on 144.39 MHz. This signal is limited to "line of sight" distances (~5-10 miles). Much larger distances are achieved by having the signal repeated through the metropolitan APRS LAN consisting of many amateur radio operators located throughout the city. A second vertical whip antenna is used for voice communication.