What is an OSM file?
An .OSM file is an OpenStreetMap Map data file. It contains geographic data like nodes, ways, and relations that define streets, buildings, and points of interest. The OpenStreetMap project uses these files to store and distribute map information. The data inside is written in plain text using the standard XML format.
How to open OSM files?
Standard text editors can open .OSM files because they are structured as XML text. You can read the raw data using Notepad++ or Visual Studio Code. To view the actual map geometry visually, you need specialized Geographic Information System (GIS) software. Popular desktop tools include JOSM (Java OpenStreetMap Editor) and QGIS.
Best practices and troubleshooting
Map files can become very large. If you download a whole city or country, the .OSM file might reach multiple gigabytes in size. This will freeze or crash most standard text editors. For massive datasets, experts prefer the compressed .PBF format. If you must process large .OSM files, use command-line tools like Osmium or Osmosis to filter or split the data before opening it.
Software and tools
viewer.online/osm analyzes .OSM files to identify their exact format and creator software, shows which programs can open the file, and usually previews it. If an .OSM extension belongs to a different software ecosystem, this tool will help you identify the actual file type.
Summary
Because .OSM files use the known XML format, viewer.online/osm can safely open and display them online, eliminating compatibility problems.