Coordinate systems sound scary, but the idea is simple. In short, they tell software what your numbers mean. So this guide explains coordinate systems, EPSG codes and WGS84 in plain English.
A coordinate is just a pair of numbers. However, the numbers mean nothing on their own. So coordinate systems give them meaning. As a result, the software knows where the point sits on Earth.
There are two kinds. Geographic systems use degrees of latitude and longitude. Projected systems use metres on a flat map. So one measures angles, and the other measures distance.
WGS84 is the common geographic system. GPS uses it. Web maps use it. So most lon/lat data is WGS84. Also, its EPSG code is 4326, which you will see everywhere.
Degrees are great for global data. However, they are awkward for local measurement. So surveyors switch to metres. That is where projected systems come in.
Every system has a number. That number is its EPSG code. So instead of a long name, you type a code. For example, 4326 for WGS84, or 3857 for Web Mercator. You can look any code up at epsg.io.
Two projected systems are common. UTM splits the world into zones and uses metres. Web Mercator, EPSG:3857, is what most web maps draw in. So both trade global accuracy for local convenience.
A mismatch puts data in the wrong place. For example, metres read as degrees fly far away. So always know your data's system. Then reproject when a tool expects a different one.
You do not need heavy software. For example, the coordinate converter shows WGS84, UTM and Web Mercator at once. Also, tools like CSV to KML let you set the system before export. In short, coordinate systems are just labels that keep your data honest.
Coordinate systems tell software what a pair of numbers means, so it can place the point correctly on Earth. Geographic systems use degrees of latitude and longitude, while projected systems use metres on a flat map.
WGS84 is the world's common geographic coordinate system, used by GPS and web maps. Its EPSG code is 4326. Most latitude and longitude data you meet is in WGS84.
An EPSG code is a short number that names a coordinate system, so you do not have to write its full definition. For example, 4326 is WGS84 and 3857 is Web Mercator. You can look codes up at epsg.io.
Geographic systems measure angles in degrees and suit global data. Projected systems, like UTM or Web Mercator, measure distance in metres and suit local measurement and web mapping.
Identify the data's real system, then reproject it to the one your tool expects. Web maps usually want WGS84 (EPSG:4326). A browser-based converter can set or reproject the system during export.
