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Using GPS for Urban Forest Inventories

Publication Number: IS2009
View as PDF: IS2009.pdf
Sea Grant Mississippi-Alabama

The following information is about using GPS during urban forest inventories. Specifically, we focus on marking waypoints (i.e., geo-coordinates) to record the locations of sample plots and trees. This information was written using the Garmin eTrex 10 as a model, although most current handheld GPS units are similar.

Main menu

The Power On button is usually on the side of the device. Sometimes it is labeled light. Press the light  button to change screen visibility. Press Back  to return to a previous screen. From the main menu screen, toggle to the satellite icon and press Enter  (Enter  is pressing straight down on the toggle button. The GPS unit must be receiving from at least three satellites.




Marking Current Waypoint

From the menu screen, select Mark Waypoint . Once in the waypoint screen, the GPS uses a default name for the waypoint. Note the GPS coordinates in the location window. Toggle to Done  and Enter  to save waypoint.


Managing Waypoints

Use Waypoint Manager to view waypoints. These points may have been generated by the unit itself or uploaded to the device from an external computer. From the menu screen, toggle to Waypoint Manager . By default, the most recently created waypoint is at the top. Note the time and date created. Marker, name, coordinates, and notes can be modified by toggling to the respective window to highlight, pressing enter to initiate the keyboard, and toggling to letters and numbers on the keyboard. After selecting a letter/number, press enter. Because this is a laborious process, we suggest editing in the office instead of the field whenever possible. A waypoint can be deleted by selecting the waypoint, pressing Menu , selecting Delete , and then selecting Yes . To delete all waypoints, in Waypoint Manager , select Menu , then select Delete all.



Setup Compass Heading

Make sure compass is on heading, not bearing. To change to heading, from the main menu screen, select Compass, press menu, select Setup Heading. A new window appears. In the Go to Line window, select Course. Press Enter.


Navigating to a waypoint

From the menu screen, toggle to Where To and Enter. Select Waypoints. Select specific waypoint. Note distance from current location and direction. Select Go. Start with an aerial image (e.g., Google Maps) of the general area. Navigate to within a reasonable walking distance of the known location of the destination. At this point, use the GPS device to walk within 30 feet of the destination. Modern handheld units can usually navigate to within 30 feet because error in the GPS system limits accuracy. More advanced, higher-priced devices, such as those used by civil engineers, have less error.


Using the compass to navigate

To use the compass, first return to the main menu screen. Select compass, then follow the compass noting the GPS heading, course line (indicates the direction you are currently heading), course pointer (indicates direction you should head), and distance to destination.





Information Sheet 2009 (POD-04-15)
By Jason Gordon, Assistant Extension Professor, Forestry

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