GIS Clip Tool: Clip Vector Layers to a Boundary

What the clip tool does

Clip is one of the most used tools in GIS. You give it two layers. The first one is the input layer: the data you want to cut, for example roads, rivers, bus stops or land parcels. The second one is the clip layer: one or more polygons that describe your area of interest, for example a city boundary or a project site. The tool works like a cookie cutter. It keeps only the parts of the input that fall inside the clip polygons and throws away everything outside.

The output has the same geometry type as the input. Clipped roads are still lines, clipped bus stops are still points, and clipped parcels are still polygons. A road that crosses the boundary is cut exactly where it crosses, and only the inside piece is kept. The attribute table of the input is copied to the output unchanged, so a road keeps its name, its type and every other field. The clip layer only gives its shape. Its own attributes are not added. This is the same rule the Clip tool follows in ArcGIS Pro, in ArcMap and in QGIS.

I built this tool for the many small clip jobs that do not justify opening a desktop GIS. You can drop a zipped Shapefile, GeoJSON, KML, KMZ, GPX or WKT file on the map, or draw your own shapes and clip rectangles. Pick the input and the clip layer, click Clip, and download the result. The whole calculation runs in your browser with open source geometry libraries, so your files never leave your computer. The map starts without a basemap to stay fast and keep the focus on your data. You can switch on a street or satellite basemap at any time.

Supported file formats

You can load several files at once, and you can mix formats. Each file becomes its own layer in the Layers panel. A layer can hold points, lines and polygons at the same time, and every one of them is clipped with the right method.

Each file can be up to 50 MB. For very large national datasets, a desktop GIS is still the better choice. See the comparison further down this page.

Technical details

Here is exactly what the tool does with your data. If you know the Clip tool in ArcGIS Pro or QGIS, most of this will look familiar.

Input geometry types

Point, MultiPoint, LineString, MultiLineString, Polygon and MultiPolygon. A single layer can mix all of them.

Clip geometry types

Polygon and MultiPolygon, with or without holes. A layer that has no polygons cannot be picked as the clip layer.

Several clip polygons

All polygons of the clip layer are merged (dissolved) into one mask before clipping. Where clip polygons overlap, the input is still cut only once, so you get no duplicate features.

Attributes

Every attribute of the input feature is copied unchanged. Attributes of the clip layer are not added (use the Polygon Intersection Tool if you need them). As an option, the tool adds clip_status (inside or clipped), clip_area_m2, clip_length_m or clip_points.

Coordinate system

WGS84 longitude and latitude (EPSG:4326), the same as GeoJSON. A zipped Shapefile with a .prj file is converted to WGS84 when it loads.

Geometry model

Cutting is done on a flat plane in degrees, the same model that Turf.js and most web GIS libraries use. Areas and lengths in the results panel are measured on the sphere (geodesic), in square metres and metres.

Boundary rule

A point that lies exactly on the clip boundary is kept. A line piece that runs along the boundary is also kept. ArcGIS and QGIS follow the same rule.

Elevation (Z)

Existing Z values stay on their vertices. A new vertex created where a line is cut gets a Z value interpolated between its two neighbours.

Multipart output

If a feature is cut into several pieces, the pieces stay together as one multipart feature (MultiLineString, MultiPolygon or MultiPoint), as in ArcGIS Pro. Tick "Split multipart results" to get one feature per piece.

Invalid geometry

If one input feature has broken geometry (for example a self-crossing polygon), that feature is skipped and counted, and the rest of the layer is still clipped.

Limits

50 MB per file. You can upload several files at once. Speed depends on your device. Tens of thousands of features usually clip in about a second.

Privacy

Everything runs in your browser. No file and no geometry is sent to a server.

How to use the clip tool, step by step

Here is the whole workflow with the built-in sample data. Your own files work the same way.

1

Step 1: Open the tool

The map opens empty and without a basemap, so nothing loads that you do not need. The toolbar has Point, Line, Polygon and Clip Rectangle drawing tools, an Upload button and a Sample Data button.

2

Step 2: Add an input layer and a clip layer

Drag and drop your files onto the map, or click Upload. Here I clicked Sample Data: it adds a city layer with parcels, roads and points, and a study area polygon with a lake cut out of it.

3

Step 3: Pick the layers and options

In the Clip panel, choose the input layer (the data to cut) and the clip layer (the polygon boundary). Only layers with polygons appear in the clip list. Choose whether you want the extra clip_status, area and length fields, and whether multipart results should be split.

4

Step 4: Click Clip Layer

The result appears as a new layer in solid color, and the input layer is hidden. The results box shows how many features went in and came out, how many were fully inside, cut at the boundary or dropped, and the total area, length and point count that was kept.

5

Step 5: Check the result with a basemap and the attributes

Tick "Show basemap" to see the result on a street or satellite map. Click any clipped feature to open its attributes. The original fields are all there, plus the optional clip fields.

6

Step 6: Download the clipped layer

In the Export panel, pick the layer and download it as GeoJSON, KML or CSV with a WKT column. The small arrow next to each layer in the Layers panel is a quick GeoJSON download.

How to clip a polygon (and lines and points)

The idea is the same in every GIS program: one layer is cut, another layer does the cutting. Here is how to clip a polygon layer in this tool, in ArcGIS Pro, in ArcMap and in QGIS, and how to do it in a script with arcpy.

The same clip in code

If you clip the same kind of data every week, a script saves time. These examples all cut a roads layer to a study area polygon.

import arcpy

arcpy.env.workspace = r"C:\data\city.gdb"

# ArcGIS Pro: Analysis toolbox > Extract > Clip
arcpy.analysis.Clip("roads", "study_area", "roads_clip")

# Older ArcMap syntax (same tool, old name)
arcpy.Clip_analysis("roads", "study_area", "roads_clip")

# QGIS Python console: Vector > Geoprocessing Tools > Clip
processing.run("native:clip", {
    "INPUT": "C:/data/roads.shp",
    "OVERLAY": "C:/data/study_area.shp",
    "OUTPUT": "C:/data/roads_clip.gpkg",
})

# GDAL / OGR command line
ogr2ogr -clipsrc study_area.shp roads_clip.gpkg roads.shp

# GeoPandas
import geopandas as gpd
roads = gpd.read_file("roads.shp")
area = gpd.read_file("study_area.shp")
roads_clip = gpd.clip(roads, area)

My take: for one clip on a normal sized file, this tool is the fastest way from file to result. For clips that repeat or run inside a bigger workflow, write an arcpy or PyQGIS script once and reuse it.

How the tool works, step by step

This is the path your data takes from the moment you click Clip Layer. Every step runs in your browser.

1. Read and clean the input. Every file is turned into GeoJSON features in WGS84. A GeometryCollection is split into separate features that share the same attributes, so the clipper only ever sees simple geometry types.
2. Dissolve the clip layer. All polygons of the clip layer are merged into one geometry, the mask M, with a polygon union. Holes stay holes. Because overlapping clip polygons become one shape, a road inside two overlapping clip polygons is still kept only once.
3. Quick bounding box test. The tool compares the bounding box of each input feature with the bounding box of M. If the two boxes do not touch, the feature cannot be inside, so it is dropped at once without any detailed math. On large layers this skips most of the work.
4. Clip points. Each point is tested with a point-in-polygon test against M. Points inside or on the boundary are kept. For a MultiPoint, only the inside points stay.
5. Clip lines. Each line segment is tested against every edge of M that is near it. The tool finds every place where the segment crosses an edge and cuts it there. Then it looks at the middle of each small piece: if the middle is inside M, the piece is kept. Pieces that touch each other are joined again into one line.
6. Clip polygons. Each polygon is intersected with M by a sweep-line boolean algorithm (Martinez-Rueda). This returns the exact shared area, including new holes where M has holes.
7. Copy attributes and add fields. Each output feature gets a copy of all attributes from its input feature. If you asked for it, the tool adds clip_status and the kept area, length or point count. If you ticked the multipart option, multipart results are split into single parts here.
8. Report and draw. The tool counts features that were fully inside, cut at the boundary, dropped or skipped, sums the kept area and length, and adds the result as a new layer on the map. The input layer is hidden so you can see the result clearly.

The steps are split this way because each geometry type needs different math. Points only need an inside/outside test. Lines need crossing points. Polygons need a full boolean overlay. Using the cheapest correct method for each type keeps the tool fast.

The theory and math behind clipping

Clipping looks simple on a map, but it rests on a few classic results from computational geometry. Here they are, in the order the tool uses them.

Clip(A, M) = { a ∩ M  :  a ∈ A  and  a ∩ M ≠ ∅ }

M = M₁ ∪ M₂ ∪ … ∪ Mₖ     (all clip polygons, merged first)

Point P = (x, y). Edge from (xi, yi) to (xj, yj).

The edge is crossed when:
  (yi > y) ≠ (yj > y)
  and  x < xi + (y − yi) · (xj − xi) / (yj − yi)

P is inside  ⇔  the number of crossed edges is odd

Segment:  P(t) = p + t · r,   r = q − p,   0 ≤ t ≤ 1
Edge:     E(u) = a + u · s,   s = b − a,   0 ≤ u ≤ 1

cross(v, w) = v.x · w.y − v.y · w.x
w = a − p

t = cross(w, s) / cross(r, s)
u = cross(w, r) / cross(r, s)

Real crossing  ⇔  0 < t < 1  and  0 ≤ u ≤ 1
cross(r, s) = 0  ⇔  segment and edge are parallel

Road:  p = (−5, 5)   q = (15, 5)   r = (20, 0)

Piece (t)      Middle x   Test          Kept
0.00 – 0.25    −2.5       outside       no
0.25 – 0.45     2.0       inside        yes → (0, 5) – (4, 5)
0.45 – 0.55     5.0       in the hole   no
0.55 – 0.75     8.0       inside        yes → (6, 5) – (10, 5)
0.75 – 1.00    12.5       outside       no

Result: MultiLineString [ (0,5)–(4,5) , (6,5)–(10,5) ]

Ring area (λ = longitude, φ = latitude, in radians):
A = (R² / 2) · | Σ (λ(i+1) − λ(i−1)) · sin φi |

Segment length (haversine):
h = sin²(Δφ / 2) + cos φ1 · cos φ2 · sin²(Δλ / 2)
d = 2R · asin(√h)

R = 6 371 008.8 m

Best clip tool in GIS: this tool, ArcGIS Pro and QGIS compared

People often ask me which is the best clip tool in GIS. The honest answer is that it depends on the job. Here is a side-by-side view.

My recommendation: if you already have ArcGIS Pro and your data lives in a geodatabase, use Clip or Pairwise Clip there. The results integrate with the rest of your project, and arcpy lets you repeat the job. If you want a full desktop GIS at no cost, QGIS has an excellent Clip tool and reads almost any format.

This tool wins when speed from file to result matters more than anything else: a colleague sends you a KML or a zipped Shapefile, you need only the part inside a site boundary, and you do not want to install or open anything. It is also handy on a computer where you cannot install software, and it is a clear way to learn what Clip does, because you can see every step on the map.

10 real-world use cases

Clip is used in almost every field that works with maps. These are the jobs I see most often.

1. Roads inside a city boundary. A transport planner has a national road network but needs only the roads inside one city. Clipping the network to the city boundary gives the exact road length inside the city, ready for a report or a traffic model.
2. Environmental impact assessment. Consultants clip habitat maps, protected areas and wetlands to a project footprint or its buffer. The result shows which habitats the project touches and how many hectares of each would be affected.
3. Farm and field planning. A farmer or agronomist clips a regional soil map to the field boundaries. Each field then has its own soil polygons with their original soil attributes, which is the base for variable-rate fertiliser or seeding plans.
4. Utility networks per service area. Water, power and telecom companies clip pipe, cable or fibre lines to a maintenance district or service area. Each team gets only its own part of the network, and the clipped length helps with planning and budgets.
5. Parcels and zoning for a development site. Urban planners and real estate analysts clip parcel and zoning layers to a planned development area. The attributes, such as owner, land use and zoning code, stay with each clipped parcel.
6. Emergency planning in flood zones. Emergency managers clip buildings, schools, hospitals and roads to a flood zone or evacuation zone. The output is the list of assets at risk, with their attributes, which can go straight into a response plan.
7. GPS tracks inside a park. Park rangers and hikers clip GPX tracks to a national park or nature reserve boundary. This shows how many kilometres of a route really run inside the park, with elevation values kept on every point.
8. Forestry and harvest blocks. Foresters clip forest stand polygons to a harvest block or an administrative unit. The clipped stands keep their species, age and volume attributes, and the clipped area feeds straight into the harvest calculation.
9. Smaller files for web maps. Web developers often start from a large national GeoJSON or Shapefile. Clipping it to the region the map shows can cut the file size a lot, which makes the web map load much faster.
10. Research and teaching. Researchers clip survey points, sample sites or trajectories to their study area before running statistics. Teachers use the tool in GIS classes because students can see clip work on the map without installing any software.

Frequently asked questions

Twenty questions people ask about clipping in GIS, with direct answers.

Libraries used and credits

This tool is built on open source software. Many thanks to the people who wrote and maintain these projects.

• Leaflet 1.9 · BSD-2-Clause · Volodymyr Agafonkin and contributors
  Draws the interactive map, the layers, the drawing tools and the popups.
• Turf.js 7 (@turf/intersect, @turf/union, @turf/area, @turf/boolean-point-in-polygon) · MIT · Turf authors
  Polygon intersection for clipping polygons, union for dissolving the clip layer, geodesic area, and the point-in-polygon test.
• polyclip-ts · MIT · Luiz Felipe Machado Barboza, based on polygon-clipping by Mike Fogel
  The boolean polygon engine behind Turf's intersect and union. It uses the Martinez-Rueda sweep-line algorithm with arbitrary-precision math.
• point-in-polygon-hao · MIT · Rowan Winsemius
  The fast point-in-polygon test that decides which points and line pieces are inside the clip area.
• shpjs · MIT · Calvin Metcalf
  Reads zipped Esri Shapefiles (.shp, .shx, .dbf, .prj, .cpg) in the browser.
• proj4js · MIT · proj4js contributors
  Converts projected Shapefiles to WGS84 using their .prj file (used by shpjs).
• @tmcw/togeojson · BSD-2-Clause · Tom MacWright
  Converts KML and GPX files to GeoJSON.
• JSZip · MIT or GPL-3.0 · Stuart Knightley
  Opens KMZ archives to read the KML file inside.
• @terraformer/wkt · MIT · Terraformer contributors
  Reads WKT input and writes the WKT geometry column in the CSV export.
• OpenStreetMap, Protomaps (hosted by KONAKTIVE), CARTO, Esri World Imagery · ODbL / provider terms · OpenStreetMap contributors, Protomaps, KONAKTIVE, CARTO, Esri
  Basemap tiles and imagery, shown only when you turn the basemap on.

The line clipping step (splitting segments at boundary crossings and testing each piece) was written for this tool. The clip engine is checked by automated tests that cover lines through holes, lines along the boundary, points on the edge, polygons over holes, overlapping clip polygons and Z interpolation.

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