How does a point-in-polygon test work?

It casts a ray from the point and counts how many polygon edges it crosses. An odd count means the point is inside, because each crossing switches between inside and outside. Holes fall out of the same rule for nothing extra.

Does this handle polygons that cross the antimeridian?

Only if the polygon is already split at 180 degrees, which is what RFC 7946 asks for. A shape whose coordinates run past ±180 will be tested as drawn, which is rarely what you want near the date line.

What happens to a point exactly on the polygon edge?

It is reported as a boundary hit rather than forced either way, because the answer there is a matter of convention rather than geometry. The tolerance controls how close counts as on the edge.

Can I test hundreds of coordinates at once?

Yes. Each line is tested against every polygon in the document, and the results table names the shape that matched. The whole run happens in the page, so a long list stays fast.

Is this accurate for large countries or continents?

The test is done on the flat latitude and longitude plane, which is exact for the inside-or-outside question as long as the polygon edges are treated as straight in those coordinates — the same assumption GeoJSON itself makes.

Point in Polygon Checker

Paste a GeoJSON polygon and a list of coordinates to see which points fall inside it.

The Point in Polygon Checker runs entirely in your browser. Boundaries and coordinates, which are often sensitive location data, are tested on your device and never uploaded.

Open the GeoJSON Viewer

About Point in Polygon Checker

Checking whether a coordinate falls inside a shape is the question behind every geofence, delivery zone and catchment area, and it is easy to get subtly wrong. This tool runs the even-odd ray cast against every polygon in a GeoJSON document and reports each point as inside, outside or sitting on the boundary. Interior rings behave the way the specification says they should: a point inside a hole comes back outside. Coordinates can be typed the way people write them, latitude first, or in the longitude-first order GeoJSON itself uses, and the results can be copied back out as a GeoJSON FeatureCollection to draw on a map.

Features

Reads Polygons, MultiPolygons, Features, FeatureCollections and GeometryCollections
Holes subtracted, so a point in an interior ring reports as outside
Boundary hits reported separately, with a tolerance you can widen
Accepts lat/lng or lng/lat input order, plus WKT POINT and geo: URIs
Tests a whole list of coordinates at once and names the shape each one matched
Hemisphere letters such as N, S, E and W override the declared order
Results exported as GeoJSON with the verdict on each feature

How to use the Point in Polygon Checker

Paste the polygon or FeatureCollection you want to test against
Enter the coordinates to check, one per line
Set whether your coordinates are latitude first or longitude first
Read the verdict per point, and export the results as GeoJSON if you need them on a map

Example

Input

51.5074, -0.1278

Output

inside — Central London

Each point reports the named feature that contains it, so overlapping zones stay distinguishable.

Common errors & troubleshooting

Every point comes back outside. — The coordinate order is almost certainly reversed. GeoJSON stores longitude first, while people type latitude first — switch the order toggle and the results will flip.
A point that should be inside reports as on the boundary. — Rounded coordinates land within a hair of the edge. Widen the edge tolerance, or use full precision for the point.
No polygons are found in the document. — Only Polygon and MultiPolygon geometries can contain a point. A LineString or Point layer has nothing to test against, and features that lost their geometry column carry only properties.
A point inside the shape reports as outside. — Check whether it is inside a hole. Rings after the first in a Polygon are interior rings, and the specification treats them as cut out of the shape.

Frequently asked questions

How does a point-in-polygon test work?: It casts a ray from the point and counts how many polygon edges it crosses. An odd count means the point is inside, because each crossing switches between inside and outside. Holes fall out of the same rule for nothing extra.
Does this handle polygons that cross the antimeridian?: Only if the polygon is already split at 180 degrees, which is what RFC 7946 asks for. A shape whose coordinates run past ±180 will be tested as drawn, which is rarely what you want near the date line.
What happens to a point exactly on the polygon edge?: It is reported as a boundary hit rather than forced either way, because the answer there is a matter of convention rather than geometry. The tolerance controls how close counts as on the edge.
Can I test hundreds of coordinates at once?: Yes. Each line is tested against every polygon in the document, and the results table names the shape that matched. The whole run happens in the page, so a long list stays fast.
Is this accurate for large countries or continents?: The test is done on the flat latitude and longitude plane, which is exact for the inside-or-outside question as long as the polygon edges are treated as straight in those coordinates — the same assumption GeoJSON itself makes.

Related tools

GeoJSON Viewer & Validator — Paste or drop GeoJSON to validate it and see its features on a map, with feature counts and a bounding box.
GeoJSON Bounding Box — Get the bounding box, centre, area and length of any GeoJSON, in both coordinate orders.
Distance Between Coordinates — Measure the great-circle distance between two latitude/longitude points in km, miles and nautical miles, with bearing and a map.
GeoJSON Simplify — Thin dense GeoJSON lines and polygons with Douglas–Peucker at a metre tolerance.
WKT to GeoJSON — Convert WKT (Well-Known Text) to GeoJSON and back, in your browser.
Coordinate Converter (DMS & Decimal) — Convert coordinates between decimal degrees, DMS and degrees-decimal-minutes, both ways, in your browser.