GSHHS shorelines are in latlon but can be imported to any location with any projection apart from unreferenced XY projection. Reprojection is done on the fly during import.
Shorelines are imported as lines, not boundaries.
The categories in layer 1 refer to the type of shoreline: 1 = land, 2 = lake, 3 = island in lake, 4 = pond in island in lake. The field type is set to these descriptions. All lines of the same type have the same category. The categories in layer 2 refer to the GSHHS ID of each imported line. Each line has as category value the GSHHS ID in layer 2, that may be useful for further processing. An attribute table for layer 2 is not created.
The -r flag restricts the import to the current region, otherwise the full dataset is imported. With the -r flag, any line that falls into or overlaps with the current region is imported. Lines are not cropped.
The 5 available resolutions are:
The generated table for layer 1 allows a fast query of the shoreline type. If needed, a table for layer 2 can be added with v.db.addtable. The new table can be populated with category values from layer 2 (GSHHS line ID) with v.to.db. Shoreline type can be uploaded from layer 1 to layer 2 with v.to.db.
Lines can be converted to boundaries with v.type. Boundaries can be converted to areas with v.centroids.
To create a land mask, extract all lines with category = 1 in layer 1, convert them to boundaries, add missing centroids, convert area vector to raster. Accordingly for lakes, islands in lakes, and ponds in islands in lakes.
Import of world borders and world rivers also included in the zip archive is currently not supported but works, just ignore the attribute table. These world borders and rivers may be not very accurate.
Wessel, P., and W. H. F. Smith, 1996. A Global Self-consistent, Hierarchical, High-resolution Shoreline Database. J. Geophys. Res., 101(B4), 8741-8743.
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