Map Editor User Guide - Importing Map Data
A map viewer is of no use unless you can import your map data into it. There are many existing file formats for map data and Map Editor supports a few of the most common. It is possible to add new file formats through the plugins mechanism.
The usual way of getting data into your map is via the Import or Import URL commands. These allow you to choose a file or URL from which the Map Editor will try and import. Typically importing a file will result in a new layer being created with the same name as the file or URL containing map features from the file, although it is also possible to import other objects such as styles or symbols. A map importer may also create other objects in the map which it needs to make use of the imported data. For example, it may create feature styles for the features it imports. For many types of imported data, when a new layer is created, it becomes read-only and retains a reference to the import file. This reference is used to reload the layer data the next time the map is opened. You can override this behaviour by turning the layer offline which allows it to be edited and the layer features to be saved instead of the reference to the file.
Each type of map file format has its own map importer - a plugin which recognises map files and reads them, creating map objects as it thinks fit. By default, Map Editor recognises hardly any file formats - the rest are provided by additional plugins. When you ask to import a file, each registered map importer is asked if it recognises the file and whether it can import it. To do this is may take into account the file's extension, filesystem type and any magic number the file format has, Before importing, it may display a dialog asking for import options: for example whether to ignore certain feature types.
After importing features, you can assign styles to them either by setting the style on the layer or by selecting the features and choosing the Assign comand from the styles panel.
Some map importers do not simply create features but may perform special actions or create other types of object. For example, it is possible to import files containing symbols or feature styles.