Free Geography Tools

In addition to its primary function in retrieving, displaying and exporting TerraServer imagery like USGS topo maps and aerial imagery, USAPhotoMaps has some handy additional capabilities. I’ll talk about the GPS functions in another post, but here are some other useful functions available in USAPhotoMaps:

- Display coordinates in latitude/longitude (decimal or d/m/s), UTM or US National Grid

- Overlay a UTM grid on the display

- Press “L”, and USGS landmarks from the gazetteer will be labeled on the image in yellow

- Elevation data can be plotted as contours, and displayed numerically in the status bar, by downloading and processing the SDTS DEM file for the area you’re viewing; here’s the helpfile section for that procedure:

“If you select File -Elevation Data -Get Elevation Data Lat/Lon, and you don’t have CONUS.LAS and CONUS.LOS (they contain data that USAPhotoMaps uses to convert a map datum from NAD27 to NAD83), then USAPhotoMaps will automatically download them from my Web site. USAPhotoMaps zooms out to 64 meters/pixel because that’s the best way to see the 7.5 minute grid that’s put on the map. This grid delineates individual elevation data files that can be downloaded by you using your Internet browser. When you click in the middle of an area, that lat/lon is copied into the Windows Clipboard. Use your browser to go to http://www.atdi-us.com/SDTS_DL_b.htm. Then paste the latitude and the longitude (separately) into the appropriate boxes on that Web site. Then you’ll see a Web page to download the data from. If 30 meter data is available, you should download it, otherwise download 10 meter data (it will be converted to 30 meter data to keep your elevation file small). After you download the elevation data file (it looks like 1627025.dem.sdts.tar.gz), select File -Elevation Data -Convert Elevation Data. USAPhotoMaps will uncompress the data, convert it to a compact format, writes it to a file named something like n40.750 w111.625 (in a sub-folder named Elevation), and create a new entry at the end of Elev.ini (which you can read with Notepad).
In Elev.ini, Zone refers to the UTM Zone. The UTM numbers are the top left UTM coordinates of the data corrected from the old NAD27 to the more accurate NAD83 datum. Name is the top left Lat/Lon of the data (using the old NAD27 datum), and is the name of the data file in the Elevation sub-folder. Spacing is the spacing between data points in meters (and is always 30).

Once you have elevation data for an area, contour lines in that area can be toggled on and off by pressing the C key (between Zoom levels 1 and 8). They’re 20*zoom feet apart (e.g. 160 feet apart at 8 meters/pixel). The lowest elevation contour lines on the screen are green, and the color is graduated to the highest elevation contour lines, which are tan-colored. The contour lines get less accurate as you zoom out.”

- Move the cursor to a point, depress the Ctrl key, then move the cursor to another point; USAPhotoMaps will draw a line between the two, and give you the distance and bearing from the first point to the second. Press Esc to remove the line.

- Press the “X” key, and the cursor’s position will be displayed in a separate box; you can select and copy the position data to paste it elsewhere.

- Move the cursor to a location, press and hold the Shift key, then move the cursor to draw a white screen on the screen. This line will define the orientation of notation text you can enter, and which is saved for future use (see the helpfile for more info).

- Select Help => Get Date of Photo/Topo, and the Terraserver web page for that image will be opened, showing you the date of both the topo image and the aerial imagery.

- Press the “S” key, and USAPhotoMaps will download and convert the current US Census TIGER road map data for the county the current on-screen location is in. Once the data is downloaded and converted (and that only has to be done once for any county), you can plot TIGER road data on the screen using the View => Tiger Streets menu option:

Move the cursor to a TIGER intersection node (the white dots above), and the street names at that intersection will be displayed. You can also type a screen name into the box at the upper right, and have it displayed on the map.