Files

There are a large variety of file formats available for GIS work. This is really more of a problem than a benefit as it requires files to be converted from one format to another to be used in different software applications. As each file has different features this mean information and even data can be lost in the conversion process. We recommend keeping vector data in Shapefiles or a spatial data base and keeping raster data in Tagged Image File Format (TIFF) files. These formats are widely supported, provide metadata and reference system information, and support a wide variety of data types and accuracy.

- What people need to know: what file types BlueSpray supports (so they can convert them if needed), how to transfer data to and from other applications (ESRI, DIVA, GRASS, MapInfo, PhotoShop, etc.).

Vector File Formats

Coverages - Old ESRI format that does maintain topological relationships but is being obsoleted by ESRI and is a proprietary format.

Shapefiles - Originally created by ESRI but now an industry standard, Shapefiles are by far the most widely used format.

STDS - The new US standard for vector data. The format supports just about everything you could imagine but is very complex an difficult to implement. Thus, it is only slowly being adopted.

Raster File Formats

TIFF - The Tagged Image File Format. Supports just about everything you could want in a raster format. Because of TIFF's complexity it took a while to be adopted but is now well supported by almost all imaging applications including GIS applications. TIFF supports both the JPEG and LZW compression techniques described below. We recommend TIFFs to store any rasters you are working on.

GeoTIFF - This is an extension to the existing TIFF format that allows a TIFF file to contain a reference system. If you save a TIFF file and check "?" in the dialog that appears to save the file as a GeoTIFF.

JPEG - The Joint Photographic Expert's Group format. This is a format for "photographic-like" images including; aerial and satellite photographs. Hill shades are another example of "photographic-like" images that can be compressed with JEPG. JPEG allows a variable compression to be set from 0 (no compression) to 100 (a lot of compression). JPEG is a "lossy" compression format and you'll see square blocks appear in your images and other distortions if you use a lot of compression or use JPEG on "drawing-like" images. JPEG is supported on the web.

GIF - Graphic Interchange Format is the original format for publishing "drawing-like" images on the web. This includes charts, drawings, and icons. GIF includes the LZW compression which is not lossy and compresses "drawing-like" images very well. It does not compression "photographic-like" images well and these images can even become larger with GIF. GIF also allows simple animations to be published on the web.

PNG - Portable Network Graphics was created to replace GIF when a patent on LZW was enforced during the 1980's. Since the patent was later released we now have two very similar formats for "drawing-like" images, both of which are well supported on the web.

NetCDF

Rasters: TIFF, PNG, JPEG, GIF?

- Can be georeferenced by adding a "WorldFile" and a "PRJ" or "WKT file.

Georeferenced raster files: GeoTIFF, NetCDF? HDF? DEM, BIL, BSQ, BSP, DIVA, GTOPO?

Vector data formats: Shapefile, text files