Draw polygons on the map, or upload a GeoJSON file or a zipped Shapefile, and find the center point of each polygon with one click. Every layer can get its own color. Save the center points as a GeoJSON file — fast, in your browser, with no extra program needed. Open in full screen ↗
What Is a Centroid, and Why You Need One
A centroid is the center point of a shape. For a simple round or square shape, this point is easy to guess. But for a real polygon, like a city block, a farm field, or a country border, the center point is not always where you think. This tool finds that point for you, for one polygon or for many polygons at the same time.
Layer Colors and Marker Style
Two color settings help you tell layers apart on the map:
- Polygon Layer color: each polygon layer gets its own color when you add it. You can change this color any time from the layer row.
- Marker Color: sets the color of the centroid points before you click "Find Centroids". Change it again after, from the layer row, if you want a different look.
Every new centroid layer stays on the map on its own, next to the polygons it came from, so you can still see both at the same time.
Two Ways to Add Your Polygons
Add the polygons you want to check with one of these methods, or use both together in the same session:
- Draw on the map: Click "Draw Polygon", then click the map to add each corner. Finish the shape with a double-click, the Enter key, or the "Finish" button. All shapes you draw go into one "Drawn Polygons" layer.
- Upload a file: Click "Upload" or drag a file onto the map — a GeoJSON/.json file, or a zipped Shapefile (.zip with .shp, .dbf and .shx inside). Each file becomes its own layer.
No file ready? Click "Sample Polygons" to add a small test set. Once you have at least one polygon layer, pick it in the "Polygon Layer" list, choose a marker color, and click "Find Centroids".
Saving Your Centroid Points
Two ways to save your work are always ready in the sidebar:
- Save one layer: click the download icon next to any layer row to save only that layer as a GeoJSON file.
- Download All Layers: puts every layer on the map — polygons and centroid points together — into one GeoJSON file, with each feature marked with its layer name.
GeoJSON opens without problems in Leaflet, Mapbox GL JS, QGIS and ArcGIS, and it even shows as a live map on GitHub.
Watch: Polygon Centroid Finder in Under a Minute
Prefer to watch instead of read? This short walkthrough covers adding a polygon and finding its exact center point.
Step by Step
1Step 1
Open the tool
The map opens on a world view with no layers yet. The toolbar at the top has Draw Polygon, Upload, Sample Polygons and a basemap switch. The sidebar on the right has the centroid tool, the layer list, and the export button.
2Step 2
Draw a polygon, or use a sample
Click "Draw Polygon" and click the map for each corner. Finish with a double-click, Enter, or the Finish button. Or click "Sample Polygons" to try the tool right away with three test shapes.
3Step 3
Or upload your own file
Click "Upload" or drag a file onto the map — a GeoJSON file or a zipped Shapefile. The tool keeps only Polygon and MultiPolygon shapes and tells you if it had to leave some shapes out.
4Step 4
Pick the polygon layer
Open the "Polygon Layer" list in the sidebar and pick the layer you want to check. Only polygon layers show up here — centroid layers are not shown, since they are already points.
5Step 5
Choose a marker color
Click the color box next to "Marker Color" and pick a color for the new centroid points.
6Step 6
Click Find Centroids
The tool works out the center point of every polygon in the layer and adds a new point layer with those centroids. The map zooms to fit the new points.
7Step 7
Check and manage your layers
In the Layers list, turn any layer on or off, change its color, zoom to it, or delete it. Centroid layers are marked differently from polygon layers, so you always know which is which.
8Step 8
Try it again with another layer
Pick a different polygon layer, or add more polygons, then click "Find Centroids" again. Each run makes a new, separate centroid layer.
9Step 9
Save your results
Click the download icon on a layer row to save just that layer, or click "Download All Layers" to save every layer — polygons and centroids — in one GeoJSON file.
Common Questions
What is a centroid, in simple words?
A centroid is the center point of a shape, worked out from the average position of all its points. For a normal, round shape this point looks like the middle. For an uneven shape, it can sit in a place you would not expect, and sometimes even a little outside the shape.
Can I draw more polygons after I already found some centroids?
Yes. New polygons you draw or upload go into their own layer, or add to the current Drawn Polygons layer if that is what you pick. Pick that layer again and click "Find Centroids" to get an updated set of points.
Can I check more than one polygon at the same time?
Yes. Click "Find Centroids" once and the tool works out a center point for every polygon feature in the chosen layer, all in the same step. You get one new point layer with one centroid for each polygon.
Why does my file get rejected?
This happens when the file has no Polygon or MultiPolygon shapes at all — for example, a file with only points or only lines. Check that your source file really has closed area shapes, not just points or paths.
Is my map data sent to a server?
No. Drawing, file reading, and the centroid math all run in your own browser, using the Turf.js library. Nothing is sent to or kept on a server, so it is safe to use with private or sensitive location data.
Why can the centroid point fall outside my polygon?
This can happen with a shape that curves a lot, like a crescent or a U-shape. The math finds the average position of the whole shape, and for these unusual shapes, that average point can land in a gap that is not part of the polygon at all. This is expected and correct.
Can I use points or lines as input?
No. This tool only works with Polygon and MultiPolygon shapes, since only a closed shape has an inside area with a true center point. If your file has points or lines mixed in with polygons, those extra shapes are left out, and you get a message about how many were left out.
Can I change the color of a layer after I make it?
Yes. Every row in the Layers list has its own color box. Click it and pick a new color — the change shows on the map right away, and it does not touch any other layer.
What is inside the GeoJSON file I download?
Saving one layer gives you just the shapes from that layer. "Download All Layers" puts every layer — polygons and centroid points — into one file, and marks each shape with the name of the layer it came from.
What does a zipped Shapefile need to have inside?
One .zip file, with at least the .shp, .dbf and .shx parts of the Shapefile inside it. If the zip has more than one layer inside, each one loads as its own separate layer in the tool.
Working with Your Layers
Each polygon layer and each centroid layer you make shows up as one row in the Layers list. From that row, you can turn the layer on or off, change its color, zoom the map to it, save it as GeoJSON, or delete it. None of these actions change any other layer.
Real-World Use Cases
🏠
Property and Land Records
County land offices and real estate platforms use the centroid of a parcel to place the address pin or price label at the true middle of the property, not at a random corner.
🚑
Disaster Response and Public Health
Emergency planners find the centroid of a flood zone or a census tract to help decide where to place a relief center or mobile clinic that stays closest to the average resident inside it.
🚚
Retail and Delivery Zones
Retail chains and delivery companies turn each store's trade area or delivery zone polygon into one point, then use that point to compare drive times or plan new depot locations.
🚜
Farm Field Management
Precision farming software finds the centroid of each field boundary to set the starting point for GPS-guided tractors, drones, and irrigation pivots.
📶
Cell Towers and Network Planning
Telecom engineers find the centroid of a coverage polygon to check antenna placement, or to pick one new tower site that best serves several overlapping coverage areas at once.
🗳️
Election and District Maps
Election offices and city planners use the centroid of a district polygon to place the district number on a map, and to check how compact or spread out a voting district really is.
How the Centroid Is Found
The tool looks at all the points of a polygon and finds the average position. This is not always the exact middle you would draw by eye, but it is the mathematically correct center of mass for the shape. For a strange or long shape, the centroid can even fall a little outside the polygon — this is normal and expected.
Only Polygons Work Here
This tool only accepts closed shapes: Polygon and MultiPolygon. Points and lines do not have a center point in the same way, so they are not allowed as input. If your file has other shapes mixed in, the tool keeps only the polygons and tells you how many other shapes it did not use.
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Map tiles © OpenStreetMap contributors and Protomaps (hosted by KONAKTIVE), CARTO, Esri (satellite). Centroid math powered by Turf.js. Shapefile parsing by shpjs. Map rendering by Leaflet. All drawing, file reading and centroid calculation is local — no data is uploaded to any server.
