GOM - the Global Overlay Mapping System

Datasets Used.

The basic coastlines were generated with data included in the standard GMT package - however, as it is a while since they were updated, a number of errors exist. A more accurate dataset available to the public is called VMAP0. Vector Map (VMap) Level 0 is an updated and improved version of the National Imagery and Mapping Agency's (NIMA) Digital Chart of the World (DCW®). The VMap Level 0 database provides worldwide coverage of vector-based geospatial data which can be viewed at 1:1,000,000 scale, i.e. 1cm=10km. It consists of geographic, attribute, and textual data stored on CD-ROM. The primary source for the database is the 1:1,000,000 scale Operational Navigation Chart (ONC) series co-produced by the military mapping authorities of Australia, Canada, United Kingdom, and the United States. The complete database is available on a set of four CD-ROM's and contains more than 1,800 megabytes of vector data organized into 10 thematic layers. VMap Level 0 includes major road and rail networks, hydrologic drainage systems, utility networks (cross-country pipelines and communication lines), major airports, elevation contours, coastlines, international boundaries and populated places. VMap Level 0 includes an index of geographic names to aid in locating areas of interest. VMap Level 0 is accessible directly from the CD-ROM or can be transferred to a hard drive and used in many geographic information system (GIS) applications, including ESRI's Arc Explorer.

The VMAP0 data is Public Domain, with only the following conditions imposed:

For further information about VMAP0 and how to obtain it, visit the MapAbility.Com website.

The relief map overlays were generated using data from the world-coverage GTOPO30 dataset, details of which, and datasets from, can be found at the GTOPO website. GTOPO30 is a global digital elevation model (DEM) resulting from a collaborative effort led by the staff at the U.S. Geological Survey's EROS Data Center in Sioux Falls, South Dakota. Elevations in GTOPO30 have a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer). GTOPO30 was developed from several raster and vector sources of topographic information to meet the needs of the geospatial data user community for regional and continental scale topographic data. The GTOPO30 dataset is divided into 33 tile datasets, available for download at the GTOPO website. I processed this data into a series of 146 image tiles, each 20° x 20°. The tiles were joined together to make seamless continental images, and then re-sized and cropped to fit the map overlays.

Note: For those interested, the image tiles will soon be available for free download on the MapAbility.Com website.

GTOP datasets - Copyright Notice : 'As required by 17 U.S.C. 403, third parties producing copyrighted works consisting predominantly of the material produced by U.S. government agencies must provide notice with such work(s) identifying the U.S. Government material incorporated and stating that such material is not subject to copyright protection. The information on NGDC web pages is in the public domain with the following exceptions: The material is specifically annotated otherwise (copyright may be held elsewhere). Trademarks, logos, and trade names such as the NOAA emblem and the Department of Commerce seal are the property of the U.S. Government and are trademarks of the Commerce Department. When you use data from NGDC, we ask that you please cite the original data contributors and sources of funding, and we would appreciate a link/credit/byline, as appropriate.'