Record boundary points while walking
Capture points while walking, then refine the boundary with manual corrections and closure diagnostics.
Plot area, perimeter, and centroid calculator
Measure a plot’s area, perimeter, and centroid in your browser using GPS track points, manual coordinates, or local GPX / GeoJSON / KML files.
It works without a basemap, so you can switch to file import or manual input when the signal is weak.
Local processing
No basemap
GPS walk survey
GPX / GeoJSON / KML
HTTPS GPS
Your input stays in this browser and is not sent to a server.
What you can do
Import local files as-is
Read GPX / GeoJSON / KML directly in the browser.
See area, perimeter, and centroid together
Review horizontal area, perimeter, centroid, and the gap between the last and first point.
Work without a basemap
Use the sketch and point list in the field, even without a basemap or network.
Export in common formats
Download GeoJSON, KML, GPX, CSV, or a state JSON file.
How to use
- Start GPS recording after granting location permission, or import a GPX, GeoJSON, or KML file.
- Check point order and closure error in the point table, then fix the shape manually if needed.
- Review the area, perimeter, and centroid cards, then export in the format you need.
Sample
Build a 4-point boundary from a GPS walk
Input
Add points in this order: northwest, northeast, southeast, southwest, then return to the first point
Output
Area is about 1.2 ha, perimeter about 450 m, and the centroid is shown too. Auto-close when the closure error is within the threshold.
A GeoJSON polygon with a hole
Input
Load a polygon with an outer ring and a pond hole
Output
Show the outer-ring area minus the hole and mark the hole explicitly in the UI.
Glossary
Geodesic
A calculation method that accounts for the earth’s curvature when measuring distance and area.
Closure error
The distance from the last point back to the first. Useful for checking GPS walk quality.
Basemap
A background map. This tool does not depend on one.
Outer ring
The outside boundary of a polygon.
Hole
An excluded area inside a boundary, such as a pond or an unplanted patch.
Simplification
Reducing the number of points while keeping the shape readable.
Formulas
Perimeter = sum of geodesic distances between consecutive pointsClosure error = distance from the last point back to the firstArea = outer-ring area − hole areaArea conversion = m² → ha / acres / km²
FAQ
Can I use it without a basemap?
Yes. The sketch, point list, closure error, area, perimeter, and centroid are the key outputs, so it does not depend on external map SDKs or map tiles.
Can I use this for legal boundary confirmation?
No. This tool is for field estimates and management only. Legal boundary work requires survey results and professional verification.
Does it calculate slope-corrected area?
The default is horizontal-projection area. DEM-based slope correction is outside the scope of this version.
Which file formats are supported?
GPX / GeoJSON / KML are supported. Files are read locally in the browser.
Can I use GPS walk recording offline?
GPS depends on the device and its permission, but input processing stays in the browser. No basemap or server upload is required.
Where is the data saved?
By default, location and boundary data are not saved. If you want to keep them, export JSON or GeoJSON files.
Notes
- This is not a legal cadastral survey or boundary-confirmation service.
- The default area is a horizontal projection, not a slope-corrected surface area.
- GPS accuracy can degrade under trees, in valleys, or during bad weather. Always check closure error.
- GPS walk recording requires a secure context. Use HTTPS or localhost.
- Data is processed locally. Export a file only when you need to keep it.