Simplify Polygon Tool — Reduce Points, Keep Your Attributes

What Is Polygon Simplification, and Why You Need It

Polygon simplification removes extra points from a shape's outline while keeping its overall form recognizable. A coastline traced from satellite imagery, a country border digitized by hand, or a survey boundary collected with GPS can easily end up with thousands of points, most of which add very little to how the shape actually looks on a map. Simplifying that shape can cut its point count by 80% or more, making files smaller and maps faster to draw, without changing what the shape represents.

Understanding the Tolerance Slider

The tolerance value controls how much detail is removed. A low tolerance keeps the shape very close to the original, removing only the smallest, least noticeable zig-zags. A high tolerance removes far more detail, producing a blockier, more generalized outline. The tool shows tolerance in meters, converted automatically to the tiny coordinate values the simplification algorithm actually works with, so you never have to think in degrees:

• Tolerance slider: drag from 0 (no change) up to 1,000 meters. The simplified shape updates instantly as you move it, so you can watch the effect happen live.
• Light / Medium / Heavy presets: one-click starting points (15 m, 75 m, 300 m) if you would rather not guess a tolerance value from scratch.
• High quality mode: switches to a slower but more accurate simplification method, useful for a final export once you have picked a tolerance you like.

Your Attributes Are Never Lost

Simplifying a shape only changes its geometry — the outline's points — and never touches the information attached to it. Every property on every feature (names, IDs, categories, measurements, anything in your original data) is carried over to the simplified version exactly as it was. Click any shape on the map, before or after simplifying, to see its full attribute table and confirm nothing was dropped.

Two Ways to Add Your Polygon

Add the polygon you want to simplify using one of these methods:

• 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.
• Upload, drag & drop, or paste: Click "Upload" and choose a .geojson file or a zipped Shapefile, drag a file onto the map, or click "Paste GeoJSON" to paste raw GeoJSON text directly — no file needed.

Exporting Your Simplified Polygon

Click "Download Simplified GeoJSON" to save the current simplified shape, at whatever tolerance the slider is set to, as a standard GeoJSON file. Every feature keeps its original properties, so the file drops straight into any GIS tool, web map, or database that already understands your data's attributes.

Step by Step

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Step 1

Open the tool

The map opens on a world view with no data yet. The toolbar at the top has Draw Polygon, Upload, Paste GeoJSON, Sample Data and a basemap switch. The sidebar holds the tolerance slider, vertex stats, and export button.

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Step 2

Add your polygon

Draw a polygon, upload a GeoJSON file or zipped Shapefile, paste raw GeoJSON text, or click "Sample Data" to try the tool right away with a ready-made jagged shape.

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Step 3

See the vertex count

The sidebar shows how many points the original shape has, right after it loads.

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Step 4

Drag the Tolerance slider

Move the slider and watch the simplified shape update instantly on the map, drawn on top of a faint outline of the original for comparison.

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Step 5

Try a preset if you like

Click Light, Medium, or Heavy for a quick starting tolerance, then fine-tune with the slider.

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Step 6

Check the reduction stats

The sidebar shows the simplified point count and the percentage reduction, updating live as you adjust the tolerance.

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Step 7

Click the shape to check attributes

Click the simplified polygon on the map to open a popup with all of its properties, confirming nothing was lost.

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Step 8

Turn off the original outline if you want

Uncheck "Show original outline" for a cleaner view of just the simplified result.

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Step 9

Download your result

Click "Download Simplified GeoJSON" to save the simplified shape, with its attributes intact, at your chosen tolerance.

Real-World Use Cases

Common Questions

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Map tiles © OpenStreetMap contributors and CARTO, Esri (satellite). Simplification powered by Turf.js (using the simplify-js implementation of the Douglas–Peucker algorithm). Shapefile parsing by shpjs. Map rendering by Leaflet. All drawing, file reading and simplification is local — no data is uploaded to any server.