Record boundary points while walking
Capture points while walking and refine the boundary with manual corrections and closure diagnostics.
Plot Area, Perimeter, and Centroid Calculator
Measure plot area, perimeter, and centroid in the browser from GPS point series, 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
Input is processed 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, boundary length, centroid, and the gap between the first and last point.
Work without a basemap
Use a sketch and point list alone, even in offline-like field conditions.
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 GPX / GeoJSON / KML.
- 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 if 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 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 between the first and last point. Useful for GPS walk quality checks.
Basemap
A background map. This tool does not depend on one.
Outer ring
The outer boundary of a polygon.
Hole
An excluded area inside a boundary. It can represent a pond or empty patch.
Simplification
Reducing points while keeping the shape readable.
Formulas
Perimeter = sum of geodesic distances between consecutive pointsClosure error = distance between the first and last pointArea = outer area - hole areaArea conversion = m² → ha / acre / km²
FAQ
Can I use it without a basemap?
Yes. The sketch, point list, closure error, area, perimeter, and centroid are the main outputs, so it does not depend on external map SDKs or tiles.
Can I use this for legal boundary confirmation?
No. This 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 out of scope for 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 itself depends on the device and permission, but the 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 survey for cadastral or boundary confirmation work.
- 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. Only export files if you need to keep them.