Every beginner in GIS hits the same confusing moment: the same boundaries arrive as a shapefile, a GeoJSON file, and a KML file, and nobody explains which one to open. All three can draw the same polygons on a map, but they carry different information, break in different ways, and suit different tools. A shapefile is a veteran desktop format, GeoJSON is a web-friendly text format, and KML is a presentation format built for Google Earth. Choosing well is less about which format is newest and more about what you need the file to do next.

A shapefile is not one file but a set of files that must travel together: at minimum the .shp geometry, .shx index, .dbf attributes, and .prj projection file. Lose one and the data may fail to open or lose its coordinate system. Shapefiles also hold only one geometry type per file, so a file declared as polygons cannot properly carry point features, and field names are limited in length, which can truncate long column names. Despite those limits, shapefiles remain the safest default for desktop work in QGIS or ArcGIS, because almost every tool reads them and they handle large vector datasets reliably. If you work mainly on the desktop and need attributes for analysis, start here and keep the whole file set zipped together.

GeoJSON stores geometries and attributes in a single human-readable text file using JSON, the same structure web developers use everywhere. That makes it the best choice for web maps built with Leaflet, MapLibre, or Mapbox, and for sharing data between scripts, notebooks, and APIs. You can open a small GeoJSON in a text editor and read its coordinates and properties directly, which is handy for debugging. The trade-off is size: GeoJSON is uncompressed text, so very large datasets become slow to load in a browser, and it always uses WGS 84 longitude and latitude, so data in another projection must be reprojected first. For small to medium datasets and anything destined for the web, GeoJSON is usually the right call.

KML was developed for Google Earth, and it excels at presentation: placemarks, styled lines, filled polygons, images, and guided tours that look good when opened. That strength is also its limit. KML is designed for display rather than analysis, so attribute handling is weaker, complex styling can bloat the file, and some GIS operations need the data converted to another format first. Use KML when the goal is to show someone a place quickly in Google Earth or Google My Maps, or to share a simple route or boundary with a non-technical reader. Do not use it as your master analysis file if you plan to join tables, run spatial queries, or publish the data for reuse.

Ask where the file goes next. Desktop analysis in QGIS with attributes and joins: shapefile, or the modern single-file GeoPackage if your tools support it. Web map, script, or API: GeoJSON. Quick visual share in Google Earth: KML. When you receive data in the wrong format, convert it in QGIS with a right-click export rather than hand-editing coordinates, and always check the result: count the features, check that attributes survived, and confirm the projection. A converted file that lost half its attributes or landed in the wrong hemisphere is worse than the original, and a two-minute check catches it.

Formats are tools, not loyalties. Keep your master data in a format that preserves geometry, attributes, and projection for analysis, and export presentation copies in whatever format your audience opens most easily. That habit alone prevents most of the lost-file and broken-map problems beginners blame on the software.