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Section 3: Archiving GIS Datasets#

3.1 Preparing to Archive: Files and Formats#

As GIS data often incorporates data from a variety of sources the formats that are safest for digital preservation vary with the type of information contained within a file. In this section, recommendations are given for formatting of GIS files, databases, images, documentation, and metadata.

Significant Properties

Any archiving of GIS files should aim to preserve the following properties:

  • Coordinate reference system information
  • Geometry (e.g. point, polygon, line)
  • Attribute fields
  • For rasters - source elevation model, bit-type, colourmap, pixel type

Strictly speaking, colour is not seen as a significant property of GIS data. This tailoring of data is stored in the project file (see below) and not in the digital object itself. If data creators require that colour/styling of original data should be recorded then this should be supplied as documentation in the form of a document or image. This documentation can then be stored with the data.

3.1.1 GIS Files#

As highlighted in a 2009 DPC Technology Watch Report, "Attempts at defining a universal data model for geospatial data have been made (for example the Spatial Data Transfer Standard (SDTS)...but have not achieved widespread adoption. As a consequence, it is not possible to speak of - geospatial data - as a single type of information that can be handled by multiple, functionally equivalent applications and formats." (McGarva et al 2009, 5). As with other data types discussed in these Guides, where the original source data cannot be archived outside of the GIS software, the most suitable files to use for archiving GIS data fall into the categories of open formats (e.g. GML and KML) and widely used standards (e.g. ESRI Shapefiles).

General considerations, as outlined in the Guide-wide section on Planning for the Creation of Digital Data include ensuring that data, where possible, is not encoded or compressed.

Project Files

In many GIS applications, project files - such as .apr or .mxd. - can be created to hold data in a tailored manner that involves classification, symbolization, and annotation based upon the data content. These data views typically appear as maps, charts, or tables, or some combination thereof. In order for an end user to render this content it is necessary not only to have the project file, but also the software that supports it, the related components (possibly including software add-ons or extensions), as well as the actual data. The required use of specific software, the complexity of the project file formats, and the tenuous links to the actual data, which is often simply pointed to, put these project files at high risk for failure over time. It is therefor recommended that project files are not archived or at least are not used to hold key information relating to the associated datasets.

File Formats

  • Arc/Info export
  • Arc/Info ungen
  • ESRI Shapefile
  • Idrisi
  • GRASS
  • MIF/MID
  • NTF
  • SDTF
  • MOSS
  • VPF
  • GML
  • KML
  • ANYTHING SUPORTED BY GDAL/OGR TOOLS

Database Files

If you have external databases connected to your GIS system, for example a database containing your attribute data, then you may want to archive these as well. Details on how best to archive database data is covered in the Databases and Spreadsheets guide.

Image Files

It is NOT necessary to archive images of every single coverage in your GIS, nor is it necessary to archive images showing all of the ways you used the GIS to play with that data. Occasionally an image may have proven useful to you in a research project and, in order to document the research that you did, archiving that image might be worth more than 1,000 words of documentation. One example is an image showing lithic flakes scattered across a house floor in a pattern that you argued demonstrates lithic production was taking place on site -- that single image might be well worth including.

Further information on archiving raster images can be found in the Raster Images guide.

3.1.2 Documentation and Metadata to accompany your GIS, database, or image files

Your data set -- the GIS files, database files, and image files -- will need to be accompanied by detailed documentation as described in Sections 3.2 and 3.3. These are general guidelines and certain archives may have specific requirements for the format and content of the metadata that accompanies GIS and spatial datasets e.g. some archive may request that it is supplied as documents along with the data whereas others, e.g. tDAR, utilise interactive web forms to help users create metadata for resources they deposit.