Draw a polygon, upload a GeoJSON file or zipped Shapefile, or paste raw GeoJSON text, then drag the Tolerance slider to reduce the number of points in the shape. Compare the simplified outline against the original in real time, and download the result as GeoJSON with every original attribute kept intact — fast, in your browser, with no extra program needed. Open in full screen ↗
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.
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.
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.
Watch: Simplify Polygon Tool in Under a Minute
Prefer to watch instead of read? This short walkthrough covers uploading a polygon, adjusting the simplification tolerance, and exporting the result with its attributes intact.
Common Questions
Why is the tolerance shown in meters instead of degrees?
The simplification algorithm itself works in coordinate degrees, but a value like "0.00045" is not intuitive. This tool converts your meter value to degrees automatically, using a standard approximation, so you can think in a real-world distance instead.
What does the original outline overlay show me?
It is a faint dashed line showing the shape before simplification, drawn underneath the solid simplified result, so you can directly compare how much detail the current tolerance removes.
Can I simplify a file with multiple polygons at once?
Yes. Upload a GeoJSON file or Shapefile with many polygon features, and the tolerance slider simplifies every one of them together, at the same tolerance, in a single step.
Can I use points or lines as input?
No. This tool only works with Polygon and MultiPolygon shapes. 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.
Is my polygon data sent to a server?
No. Drawing, file reading, and the simplification 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.
What tolerance value should I use?
It depends on your shape and your goal. Start with the Medium preset (75 m) and watch how the outline changes, then adjust with the slider. A good tolerance removes visual clutter without noticeably changing the shape's recognizable form at the zoom level you care about.
Will simplifying lose my attribute data?
No. Simplification only changes a shape's geometry — its outline points — and never touches its properties. Every name, ID, category, or other value attached to a feature is carried over to the simplified version unchanged.
What does "simplify" actually do to a polygon?
It removes points from the shape's outline that add very little to its overall form, using the Douglas–Peucker algorithm. The result looks similar to the original at a glance, but stores far fewer coordinate points.
Why does my shape barely change even at a high tolerance?
Simple shapes with few points to begin with have little left to remove. Simplification has the biggest visual effect on shapes with lots of fine, jagged detail, like a traced coastline or a hand-digitized boundary.
How big a file can I load?
Files up to 50 MB are accepted. Very large files with tens of thousands of points may take a moment to simplify each time you move the slider, since everything runs in your browser rather than on a server.
What does "High quality" mode do?
It switches to a slower but more careful simplification method that tends to preserve shape better at the same tolerance value. It is worth turning on for a final export once you already know roughly what tolerance you want.
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.
Real-World Use Cases
🌐
Lighter Open Data Downloads
Open-data teams publish a simplified version of a large boundary dataset alongside the full-detail original, giving casual users a much smaller file that still looks right on a map.
🛰️
Cleaning Up Satellite-Traced Boundaries
Remote sensing teams simplify polygons traced from satellite or drone imagery, smoothing out pixel-level jaggedness while keeping the overall shape and its attached classification data.
🗺️
Faster Web Maps
Front-end developers simplify large, detailed polygons — country borders, coastlines, administrative boundaries — so a Leaflet or Mapbox GL JS map renders and pans smoothly instead of stuttering under thousands of extra points.
📊
Faster Spatial Analysis
GIS analysts simplify complex polygons before running buffer, intersection, or overlay operations, since fewer vertices means those calculations finish noticeably faster.
🎓
GIS Teaching and Learning
Students and GIS learners use the live before-and-after comparison to build an intuitive feel for how simplification tolerance actually affects a shape, instead of only reading about the Douglas–Peucker algorithm.
🖨️
Cleaner Print and Export Layouts
Cartographers simplify a shape's outline for a small-scale printed map, where fine coastal or boundary detail would just look like noise at that zoom level anyway.
📱
Smaller Mobile App Data
Mobile app teams shrink polygon files bundled with an app or fetched over a slow connection, cutting data size and load time without changing what areas the app shows.
🎮
Game and 3D Engine Boundaries
Game developers and 3D artists simplify real-world area outlines imported as level or collision boundaries, since engines run faster with far fewer points to process per shape.
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.
Step by Step
1Step 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.
2Step 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.
3Step 3
See the vertex count
The sidebar shows how many points the original shape has, right after it loads.
4Step 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.
5Step 5
Try a preset if you like
Click Light, Medium, or Heavy for a quick starting tolerance, then fine-tune with the slider.
6Step 6
Check the reduction stats
The sidebar shows the simplified point count and the percentage reduction, updating live as you adjust the tolerance.
7Step 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.
8Step 8
Turn off the original outline if you want
Uncheck "Show original outline" for a cleaner view of just the simplified result.
9Step 9
Download your result
Click "Download Simplified GeoJSON" to save the simplified shape, with its attributes intact, at your chosen tolerance.
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.
More Tools You Might Like
GeoJSON Viewer
Upload, drag & drop, or paste GeoJSON data, then view it on a map, click features for details, and change the color.
Digitize GIS Data
Draw your own points, lines and polygons by hand, and save them as GeoJSON, KML or GPX.
Polygon Centroid Finder
Draw or upload polygons, then find the center point of every polygon in one click.
Shapefile Viewer
Upload a zipped Shapefile and view every shape on an interactive map, right in your browser.
Map tiles © OpenStreetMap contributors, drawn with Protomaps (hosted by KONAKTIVE), with CARTO as the fallback. Satellite imagery: Esri. Geometry calculations: Turf.js. Simplification: simplify-js (Douglas-Peucker algorithm). Shapefile reading: shpjs. Map rendering: Leaflet. All calculations run in your browser, and nothing you enter is stored on a server.
