About these tools
Geospatial data arrives in a handful of interchange formats and a very large number of coordinate reference systems, and most of the friction in day-to-day GIS work is moving between the two. Well-Known Text is what a spatial database hands you; GeoJSON is what a web map and a JavaScript library expect. The converters here translate one into the other and back, covering points, lines, polygons, all three multi-geometries and geometry collections, so you can paste a value straight out of a PostGIS or SQL Server query and get something a browser can draw.
A coordinate on its own is not a location. It is a pair of numbers that only means somewhere once you know the coordinate reference system it belongs to, and that system is almost never carried inside the data. GeoJSON solves this by decree: RFC 7946 says coordinates are longitude then latitude in WGS 84 decimal degrees, and nothing else. WKT carries no CRS at all unless it is written as EWKT with an SRID prefix. This is why the same file can look perfectly valid and still land in the Gulf of Guinea, the usual symptom of latitude and longitude arriving the wrong way round.
The EPSG lookup exists for the other half of that problem. EPSG codes are the standard shorthand for coordinate reference systems, and knowing that 4326 is geographic degrees while 3857 is Web Mercator metres explains most of the confusion between a map service and the data being drawn on it. The lookup ships an offline subset of the registry with each system's datum, projection method, units and area of use, plus its PROJ string and WKT, so you can check what a code means without guessing from its name.
Measurements need the same care. Latitude and longitude are angles, not lengths, so the distance between two points is never the Pythagorean distance between their degrees: one degree of longitude is about 111 kilometres at the equator and near zero at the poles. The distance calculator works on the sphere or the WGS 84 ellipsoid and names which, and the area calculator computes a geodesic area from geographic coordinates rather than quietly treating degrees as metres. Where a planar calculation is what you actually want, you choose it and state the units.
The remaining tools take care of the small, repetitive jobs. The GeoJSON formatter pretty-prints or minifies a file and checks its structure against the specification rather than only its JSON syntax. The bounding box calculator produces the extent in the orders different systems expect, which are not the same: GeoJSON and most APIs write minimum longitude first, while a WMS 1.3.0 request in a geographic CRS expects latitude first. The WMS URL builder assembles a GetMap request with its parameters in the form each version of the specification requires.
Every GIS tool on this page runs entirely in your browser. Geometry, coordinates and files you open are processed by JavaScript on your own device and are never uploaded, which matters when the data is a client's site boundary or an asset location rather than a public dataset.
Frequently asked questions
Is my GIS data uploaded to your server?
No. Every tool in this section processes your input with JavaScript in your browser. Geometry, coordinates and any file you open stay on your device, and no request carrying them is sent to us. The page itself is loaded from our server, and nothing else is.
Is it longitude first or latitude first?
It depends on the format, which is why this catches people out. GeoJSON is unambiguous: RFC 7946 requires longitude, then latitude. WKT as written by PostGIS and most databases uses the same order, X then Y. Human-readable coordinates are usually quoted latitude first, and WMS 1.3.0 uses the axis order defined by the CRS, which for EPSG:4326 is latitude first.
Do these tools reproject between coordinate systems?
Only where a transformation is exactly defined and needs no datum shift: WGS 84 geographic to and from Web Mercator and UTM. Anything involving a change of datum needs a transformation grid and has real accuracy implications, so rather than guess at one, the EPSG lookup tells you what each system is and leaves the reprojection to PROJ, GDAL or your GIS.
Why is my calculated area slightly different from my GIS software?
Because of the earth model. The area calculator uses a geodesic calculation on a sphere with the WGS 84 authalic radius, which is within roughly 0.3 percent of an ellipsoidal result for most polygons. Desktop GIS usually computes on the ellipsoid or in a projected CRS chosen for equal area, so small differences are expected and are stated on the page.
What does EPSG:4326 actually mean?
It is the EPSG code for WGS 84 geographic coordinates: latitude and longitude in decimal degrees on the WGS 84 datum, which is what a GPS reports and what GeoJSON requires. It is not a projection, so it has no metres. EPSG:3857, Web Mercator, is the projected system almost every web map draws in, and its units are metres.
Can I use these tools on large files?
Within reason. Processing happens on your own machine, so the limit is your browser's memory rather than an upload size, and files of a few megabytes are handled comfortably. A very large FeatureCollection is better handled with ogr2ogr or a database than with any browser tool, including this one.