# GMT ASCII Vectors (.gmt)

OGR supports reading and writing GMT ASCII vector format. This is the format used by the Generic Mapping Tools (GMT) package, and includes recent additions to the format to handle more geometry types, and attributes. Currently GMT files are only supported if they have the extension ".gmt". Old (simple) GMT files are treated as either point, or linestring files depending on whether a ">" line is encountered before the first vertex. New style files have a variety of auxiliary information including geometry type, layer extents, coordinate system and attribute field declarations in comments in the header, and for each feature can have attributes.

## Creation Issues

The driver supports creating new GMT files, and appending additional features to existing files, but update of existing features is not supported. Each layer is created as a seperate .gmt file. If a name that ends with .gmt is not given, then the GMT driver will take the layer name and add the ".gmt" extension.