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Geometry Tools - Buffer Simplify Clip Geometries Online

Free GIS geometry tools: create buffer zones, simplify geometries with Douglas-Peucker, clip by bounding box or polygon. Process GeoJSON/WKT data instantly.

info Create a buffer zone around geometry at specified distance.

What are Geometry Processing Tools?

Geometry processing tools perform spatial operations on geographic features. These operations are fundamental in GIS analysis, cartography, and spatial data processing. This tool provides three essential operations: buffering, simplification, and clipping.

These operations are used extensively in urban planning, environmental analysis, transportation networks, and many other geospatial applications. Understanding how to manipulate geometries is crucial for effective spatial analysis.

Key operations:

  • Buffer: Create zones of influence around features (e.g., 500m around a river)
  • Simplify: Reduce geometric complexity while preserving shape (Douglas-Peucker algorithm)
  • Clip: Extract portions of geometry within a boundary or bounding box
  • Visualization: Preview results on interactive map
  • Multiple Formats: Support for GeoJSON and WKT input/output

Buffer Operation

Buffering creates a zone of specified distance around a geometry. It's one of the most common spatial operations in GIS analysis.

Buffer parameters:

  • Distance: How far the buffer extends from the original geometry
  • Unit: Meters, kilometers, miles, or feet
  • Steps: Quality of buffer curve (8-64 steps, higher = smoother but more complex)

Common buffer use cases:

  • Proximity Analysis: Find areas within distance of a feature (e.g., 1km from subway)
  • Impact Zones: Determine area affected by pollution, noise, or other factors
  • Service Areas: Identify coverage areas for facilities or services
  • Setback Regulations: Enforce minimum distance requirements in planning

Simplify Operation (Douglas-Peucker)

Simplification reduces the number of vertices in a geometry while preserving its general shape. The Douglas-Peucker algorithm is the industry standard for line and polygon simplification.

Simplification parameters:

  • Tolerance: Maximum distance a simplified point can deviate from original (lower = more detail)
  • High Quality: Uses more computation for better results (optional)

When to use simplification:

  • Map Display: Reduce detail for faster rendering at small scales
  • Data Storage: Decrease file size for large datasets
  • Web Performance: Optimize geometries for web mapping applications
  • Generalization: Create appropriate level of detail for different zoom levels

Note: Tolerance is in degrees for geographic coordinates or in the units of projected coordinates. Start with small values (0.0001-0.001 for degrees) and increase as needed.

Clip Operation

Clipping extracts the portion of a geometry that falls within a specified boundary. This is also known as 'cookie cutting' or 'spatial intersection'.

Clip methods:

  • Bounding Box: Clip by rectangular extent [minX, minY, maxX, maxY]
  • Polygon: Clip by custom polygon boundary (supports complex shapes)

Common clipping use cases:

  • Study Area Extraction: Extract data for specific region of interest
  • Administrative Boundaries: Clip features to country, state, or city limits
  • Data Subsetting: Create smaller datasets from large geographic datasets
  • Map Production: Prepare data to fit specific map extents

Algorithm Details

Douglas-Peucker Algorithm:

The Douglas-Peucker algorithm works by recursively dividing a line and removing points that fall within a specified tolerance of the line segment. It's efficient and produces excellent results for most geometries.

  • Step 1: Draw line from first to last point
  • Step 2: Find point farthest from this line
  • Step 3: If distance >tolerance, keep point and recurse on segments
  • Step 4: If distance ≤ tolerance, remove all points in between

Best Practices

Tips for effective geometry processing:

  • Buffer: Use appropriate units for your data (meters for local, degrees for global)
  • Simplify: Test different tolerances to find the right balance between detail and size
  • Clip: Validate your clipping boundary is in the same coordinate system
  • Performance: Simplify complex geometries before other operations
  • Validation: Always visualize results to ensure they meet your requirements

These operations can be combined: for example, buffer a line, then clip to study area, then simplify for web display.

Frequently Asked Questions

This tool applies common geometric operations to vector data: buffering (expanding a feature outward by a distance), simplification (reducing vertex count while preserving shape), and clipping (cutting a feature against a bounding box or polygon). It accepts GeoJSON Points, LineStrings, Polygons, MultiPolygons, and FeatureCollections, and outputs a new GeoJSON with the operation applied. Buffering is useful for proximity analysis like finding everything within 500 m of a river. Simplification reduces file size before serving tiles. Clipping isolates a region of interest. All operations run entirely client-side; nothing is uploaded.

All input GeoJSON should use WGS84 longitude-latitude (EPSG:4326), the only CRS the GeoJSON specification permits per RFC 7946. Coordinates are decimal degrees, with longitude (X) first and latitude (Y) second. If your data is in a projected CRS such as UTM, Web Mercator (EPSG:3857), or a national grid, reproject to WGS84 first using QGIS, GDAL ogr2ogr, or a coordinate-converter tool. The buffer distance you specify is measured in metres along the ground, using a geodesic calculation that accounts for Earth's curvature, so you can buffer accurately even at high latitudes.

The buffer is computed in geodesic metres rather than degrees, so the resulting shape correctly accounts for the convergence of meridians at higher latitudes. A 1000-metre buffer around a point in Oslo (60 degrees north) covers half the longitude span of the same buffer around a point on the equator, exactly as physical reality demands. Internally, the tool projects each vertex to a local azimuthal projection, offsets the boundary by the requested distance, and reprojects back to WGS84. This is more accurate than flat-Euclidean buffering, which would distort shapes badly outside the tropics.

The default is the Visvalingam-Whyatt algorithm with optional Douglas-Peucker fallback. Visvalingam-Whyatt iteratively removes the point whose triangle (formed with its two neighbours) has the smallest area, repeating until the tolerance is reached. This preserves perceptually important corners better than Douglas-Peucker, especially on coastlines and complex polygons. The tolerance is expressed in metres and roughly corresponds to the maximum displacement of any vertex from the original line. For web map tiles, 1 to 5 metres at zoom 18 down to 1000 metres at zoom 5 is typical. Topology is preserved for FeatureCollections.

GeoJSON is the open standard format for encoding geographic features (RFC 7946, published 2016). It is a JSON document with a strictly defined schema: a Feature object wraps a geometry (Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, or GeometryCollection) and a properties object. GeoJSON has become the universal lingua franca of web mapping because it is human-readable, native to JavaScript, and natively rendered by Leaflet, Mapbox GL, Google Maps, OpenLayers, and every modern geospatial tool. This tool requires GeoJSON so that operations have unambiguous geometry semantics and so that output can be pasted directly into any viewer.

A Polygon is a single closed shape defined by one outer ring (the boundary) and zero or more inner rings (holes cut out of it). A MultiPolygon is a list of Polygons that should be treated as a single feature, such as the islands of Indonesia or the disconnected territories of France. The GeoJSON specification distinguishes them so that operations behave correctly: buffering a MultiPolygon buffers each piece individually, while simplifying a Polygon preserves its single boundary. This tool handles both transparently, but you should output MultiPolygon when your feature is geographically discontinuous.

For files under 50 MB, performance is excellent and operations complete within seconds. Between 50 and 200 MB, expect 10 to 60 seconds of processing and possible memory pressure on devices with less than 4 GB of RAM. Above 200 MB, you should preprocess server-side with GDAL or Mapshaper, or split the data by region before uploading. The tool uses Turf.js, which loads the entire FeatureCollection into JavaScript objects; modern browsers cap a single tab at roughly 2 to 4 GB of heap. For massive datasets, consider streaming via newline-delimited GeoJSON processed server-side.

Floating-point arithmetic during buffering, simplification, or clipping introduces tiny rounding errors, typically in the 10th to 15th decimal place. These shifts are negligible for visualisation (less than 1 micrometre on the ground at the equator) but can cause problems in strict topological checks. If you need exact preservation, use simplification tolerance set to zero to skip that pass, or use a CRS like EPSG:3857 before processing and convert back. For most cartographic and analytical purposes, the floating-point drift is invisible.
Geometry Tools - Buffer Simplify Clip Geometries Online — Free GIS geometry tools: create buffer zones, simplify geometries with Douglas-Peucker, clip by bounding box or polygon.
Geometry Tools - Buffer Simplify Clip Geometries Online
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Geography & Mapping ToolsGEOGRAPHY & MAPPING TOOLS21
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