File Coordinate System Converter (Reproject)

Changing the coordinate system of a file

The same piece of land often reaches you in files that use different coordinate systems. Survey and cadastral data may be in a national transverse Mercator grid, older plans in ED50, and GPS tracks and web maps in WGS84. When such files are overlaid in one project without bringing them into the same system, layers end up hundreds of metres or even kilometres apart. This tool transforms the coordinates of every feature in a file into the system you choose, keeps the attributes, and returns the result in the same format.

How to use it

1. Choose a file. For a shapefile, choose the .zip archive or select the .shp, .dbf and .prj files together. GeoJSON, KML, KMZ and CSV files with X/Y columns are also accepted.
2. Check the source system. The tool reads it from the .prj file, from the crs member of a GeoJSON file, or from the KML rule that coordinates are always WGS84. If it cannot, it lists likely systems based on the coordinate range.
3. Choose the target system. For a system that is not listed, type its EPSG code or a proj4 definition.
4. Press Convert. Check on the preview map that the data lands in the right place, compare source and target values in the sample table, then download the file.

Datum versus projection

A coordinate system has two parts. The datum defines the ellipsoid that approximates the shape of the Earth and how that ellipsoid is tied to it. The projection turns latitude and longitude on the ellipsoid into flat easting and northing values in metres. WGS84 / UTM 35N and WGS84 / UTM 36N share a datum and differ only in central meridian, so converting between them is pure mathematics. Between ED50 and WGS84 the datum itself changes, and a set of transformation parameters is needed.

ITRF96, WGS84 and ED50

WGS84 is the global system used by GPS receivers and web maps. ITRF96 (TUREF) is Türkiye's current national reference frame; it uses the GRS80 ellipsoid, and large-scale maps are produced in 3° wide TM zones with central meridians 27, 30, 33, 36, 39, 42 and 45. The difference between ITRF96 and WGS84 is in the centimetre to decimetre range, and the tool applies no parameters between them. ED50 is the older European datum based on the International 1924 ellipsoid. In Türkiye the same point has coordinates about 100-200 metres apart in ED50 and WGS84. For ED50 the tool uses the seven-parameter transformation EPSG:1784 (ED50 to WGS 84 (30)) defined for Türkiye; EPSG gives its accuracy as about 2 metres. For ED50 data from other countries this can differ from the national parameters by a few metres.

Why data appears shifted

• Wrong datum: if an ED50 file is read as WGS84, the data moves by roughly 100-200 metres in Türkiye, and by similar amounts elsewhere in Europe.
• Wrong zone: if data in one TM or UTM zone is read as the neighbouring zone, it moves by hundreds of kilometres east or west. Eastings are around 500,000 in every zone, so the zone cannot be recognised from the numbers.
• Swapped X and Y: some survey conventions write northing first. If the columns are read the wrong way round, the data lands somewhere else entirely, often in the ocean.
• Missing .prj: a shapefile without a .prj file is guessed differently by different software.

Common EPSG codes

Output formats

A shapefile is written as a zip with an ESRI-style .prj for the target system and a .cpg file declaring UTF-8 attributes. A GeoJSON with mixed points, lines and polygons is split into one shapefile per geometry type. The current GeoJSON standard, RFC 7946, expects WGS84 coordinates; if the target is another system, a legacy crs member is added, and some software may ignore it. KML always uses WGS84 latitude and longitude, so it is only offered when the target is WGS84.

Data and method

Coordinates are transformed with proj4js 2.9.0 (MIT licence). System definitions come from this site's own list, checked against the EPSG registry; no request is sent to the EPSG website or any other service. Shapefiles are read with shpjs 6.1.0 (MIT), zip files with JSZip 3.10.1 (MIT), CSV with PapaParse 5.4.1 (MIT) and KML with @tmcw/togeojson 5.8.0 (BSD-2-Clause). The shapefile writer and the .prj parser are this page's own code. Basemaps belong to Esri and OpenStreetMap contributors. Open-source libraries used and their licences: Data Sources.

Accuracy limits

Projection changes within the same datum are accurate to the millimetre. The ED50 transformation is accurate to about 2 metres; work that needs centimetres, such as cadastre and setting out, should use official regional parameters. Z values are kept as they are and the height datum is not changed. Lines and polygon edges are transformed only at their vertices, so on very long edges with sparse vertices the different curvature of two projections can cause small deviations.

For questions about a specific project or a larger data migration, you can reach the team through the contact page or visit Rodosto Teknoloji.