Trace your fields, or use your GPS to instantly calculate field area

ExpertGPS calculates field acreage down to the square foot. Instantly. Without any calculations or complicated math on your part. Just click and draw. Or upload waypoints or track logs from your GPS. All you have to do is download the 30-day trial of ExpertGPS and follow these simple step-by-step instructions below.

SH asks:
I have 174 waypoints coordinates and I would like to calculate the area of the farmland based on those coordinates. How do I do that using GPS Expert?

Calculating Area of a Farm Field Marked with GPS Waypoints

Click Receive from GPS on the GPS menu in ExpertGPS. All of your GPS waypoints will be shown on the map. Use the Route Tool to connect the waypoints marking the corners of your field.

Show the Area of your Field

On the View menu in ExpertGPS, click Show Route List. Then click Select List Columns. Add the Area column. ExpertGPS displays the area of all of your fields.

Converting between Acres, Square Feet, and Hectares

To convert the area calculated by ExpertGPS between acres, square feet, hectares, or another unit, click Preferences on the Edit menu, and click on the Units tab.

Download ExpertGPS, and Calculate the Area of your Fields Now!

Download the free ExpertGPS demo and follow these simple step-by-step instructions to calculate the acreage of your land and fields.

Stacy X. asks:
What is the best method to create a gpx or kml file of an area filled polygon that has islands (a lake shp file). When I export as a gpx, it creates a polyline where the end node of the lake outline connects to the end nodes of each of the islands. When I export as a kml, the fill of the polygon is not complete. The strange part is when you zoom in, the lake polygon will fill; then if you zoom out, it empties.

ExpertGPS Pro allows you to draw, view, and import polygons with complex geometry, including filled objects with holes in them. You can use this feature to draw lakes with islands, a park boundary with private land inholdings, or other complex shapes. Here's how to create the "donut" shown at right.

Begin by drawing the outer shape, using the shape tool. I clicked to draw the four corners, and then pressed Enter to finish the drawing and connect the fourth corner back to the start. (This happens automatically when you select a filled shape type)

I then drew the inner hole using the shape tool. Add the shape points in counter-clockwise order! This is important - most GIS and 3D systems consider counter-clockwise polygons to be inner holes.

Once the two shapes are drawn, select both by clicking the outer one with the Select tool, holding Shift, and selecting the inner one (or ones, if there are multiple holes). Right click, and click Join Shapes to convert the selected shapes into one composite shape. ExpertGPS will recognize the inner holes and leave them unfilled. If you calculate area, ExpertGPS will subtract out the area of any inner polygons, giving you the correct acreage of your lake or property.

You can now export the shape to your GIS software in shapefile format, or click View in Google Earth to see the lake or property boundary over the aerial imagery in Google Earth.

Dale writes:
My application requires that I measure the areas of various land use types within a given project area. I had problems when I tried to append a particular shape of one land use to another shape of a different land use. I had to leave a gap to keep things from getting messy. I think I have that issue resolved by assigning each land use type to a different layer. I also had problems when I placed a node off location. I could not find a way to 'grab' the node and move it to the correct location (feature request). Deleting the shape and re-drawing it is a pain.

There are a couple techniques you can use if you are drawing filled objects that need to mesh right up against each other. If they have straight sides (not curved like a river centerline), it might be easiest to draw them using the route tool, and then convert the routes to shapes after. This is because the route tool automatically snaps to waypoints as you draw. So if you are drawing agricultural fields, and put waypoints at all of the field boundaries, as you use the route tool to "connect the dots" you'll get routes that align perfectly with the adjacent fields.

As you begin to draw a new route, ExpertGPS might show a + cursor, meaning that is going to extend an existing route. If this isn't what you want, hold SHIFT to override this.

You can move nodes to a new position by selecting the waypoint at that node and using the Move Selected tool to move it to a new position.

Once you've got everything in place, select the routes and click Convert to Shape on the Tools menu. You can then delete the routes and waypoints.

If you need to make changes to shapes, it's possible to do so. Click once with the select tool to select the shape, and then drag a selection rectangle over the node you want to move. It should be highlighted in magenta. Now switch to the Move Selected tool and drag to the new location.

An ExpertGPS user asks:
How do I find the center of the triangle created by three waypoints from my Garmin GPSMAP 60CSx?

The Average Waypoint command in ExpertGPS allows you to find the center (average, mean) location of any group of waypoints. To use the command, simply select three or more waypoints in ExpertGPS (on the map, or by selecting them from the Waypoint List), and click Average Waypoint on the Tools menu.

ExpertGPS creates a new waypoint "Average" at the center of the points you've selected.

Tom H. asks:
I need a software mapping program that will allow me to draw a circle of varying radius and tell me how many acres in that circle.

How do I Draw a Circle on a Map and Calculate its Acreage?

The formula for the area of a circle is: Area = π * radius². If the radius is given in feet, the area is in square feet. To convert from square feet to acres, divide by 43560. So the acreage of a circular area is: Acres = π * radius_in_feet² / 43560.

Acreage Calculator for a Circular Field

Drawing Circles on the Map

ExpertGPS can draw a circle of any radius around a waypoint. Edit the waypoint, and enter the circle radius in the Proximity field. Waypoint Proximity is used by some Garmin GPS receivers to sound an alarm when you come within the proximity distance. Mariners use proximity waypoints to mark rocks, wrecks, and other obstructions in the waterway, so that their GPS will alert them if they approach these hazards too closely. You can make use of the Proximity circles in ExpertGPS to map out center-pivot irrigation systems for your farm, check the coverage of wireless or communications towers, or determine the service area of a store or business, fire station, or police station.

Related Topics Ask the GPS Expert: How do I calculate the acreage of an irregularly-shaped farm field? Calculating the acreage of any parcel with ExpertGPS. ExpertGPS Help File: Calculating Area

Dan M. from Indianapolis asks:
You claim that your software can calculate an area. This is the application I need because I have a GPS receiver that does not calculate area but if I understand correctly I can mark different waypoints in my farm (not a perfect square) and then download them to your software and then I get the area? Do I need a topo map of my farm to do this???
Please forgive my ignorance but I just need an application that would allow me to know exactly the area in a big farm that may have for example, corn or soy, etc.
Thank you in advance for your help.

How do I Calculate the Area of a Farm Field?

You can use ExpertGPS to calculate the area of any field on your farm, and you don't need your own topo map (or even a GPS receiver) to do this. ExpertGPS will automatically calculate the area of any object you draw on the map or mark with your GPS. Let's start by drawing on the map...

Calculating Area by Drawing on the Map

The first step is to bring up an aerial photo of your farm. Download and install ExpertGPS, and start the program. Click Go to Address on the Go menu, and type in the address of your farm. ExpertGPS will recenter the topo map on your farm. Click Show Aerial Photo Map on the View menu, which should give you a pretty good view of your fields.

Now we're going to trace a field. Select the Track tool. Click once on the corner of your field, and continue clicking at each corner, working your way around the field. The track tool draws straight lines when you click. If there's an irregular edge, along a road or creek, click and drag the mouse, tracing that edge. When you've traced your way around the entire field, press Enter to finish the track. Name your field, and click OK.

Now switch to the Select tool, and click on the track of your field to select it. Right-click, and click Close Track. This tells ExpertGPS to treat this object as a closed shape. You'd use this command any time you were drawing a field, paddock, or stock pond.

On the left side of the screen, switch to the Track List. Click Select List Columns on the View menu, and make sure Area is checked. ExpertGPS will calculate the area of your field (and all the other closed tracks in the Track List) and display it. If you need to switch between acres, square feet, hectares, or other units of measure, click Preferences on the Edit menu, and change the Distance Units.

Calculating Area from a Recorded GPS Tracklog

Another way you could trace the boundaries of your field would be to take your GPS out and walk or drive the edge of the field, recording a GPS track. Back at your computer, click Receive from GPS, and ExpertGPS will bring in the track outlining your field. Follow the directions above, starting with Close Track.

Calculating Area of a Field Marked with Waypoints

If you have previously used your GPS to mark waypoints at the corners of your field, click Receive from GPS to bring them into ExpertGPS. Switch to the Route Tool, and click on each waypoint to connect them together into a route which traces the boundaries of the field. When you are done, select and right-click on the route, and click Close Route. Proceed as above to enable the Area column on the Route List.

Labelling Objects on the Map with their Area

Update - December 17, 2008: ExpertGPS User Bob C. asked a follow-up question: "How can I label an object on the map with it's area?" Here's what I did: I looked in the Area column in the Track list (as described above) to find the area that ExpertGPS calculated for that field. I then selected the field, clicked Edit Track, and entered Field 3n7.9 Acres in the field's Label. The n is a special command that causes ExpertGPS to insert a newline, making Field 3 and 7.9 Acres appear on two separate lines.

Related Topics Ask the GPS Expert: How do I determine the acreage of a field covered by a center-pivot irrigator? How do I calculate area with a GPS? ExpertGPS Help File: Calculating Area