Sustainability of Digital Formats: Planning for Library of Congress Collections

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Geospatial Content >> Quality and Functionality Factors

The factors discussed here apply to digital resources that are primarily geospatial. Geospatial resources are intended to be used in Geographic Information Systems (GIS), and computer systems or software packages that enable spatial analysis. Geospatial resources convey information about the Earth, the location of specific features, and attributes and properties of specific geo-located features. As such, geospatial resources and the formats used to represent them will usually comprise information one or more of the following three forms: raster or bit-mapped images; vector images consisting of points, lines and polygons; and data values that express attributes associated with geographic locations or features. Geospatial formats often combine the characteristics of images and datasets. Raster images may represent pixel-based datasets; vector data may include attribute information with vector-based shapes, for example, to label features such as roads, rivers, and political boundaries. Some geospatial formats consist of several component files that are stored together in a directory. Increasingly, geospatial resources are stored in geospatially focused databases that combine and relate many geospatial resources for use together.

An introduction to geospatial resources and to aspects of geospatial analysis and data documentation that geospatial formats must support is provided in a separate essay, Introduction to Geospatial Resources and Formats. This document will link to relevant sections of the Introduction to supply additional information and context.

Given that geospatial formats often have characteristics of images and datasets, factors that relate to quality and functionality of those more general content types are often relevant. Those factors, listed in the sidebar, are discussed elsewhere on this web site, in:

Format descriptions for geospatial formats will employ relevant factors from among those used to assess still image formats and dataset formats in general. For example, Support for Multispectral Bands is a functionality factor for still images that is particularly significant for geospatial images such as satellite imagery. Datasets: Normal Functionality covers support for varied data types and data structures. Support for Specialized Software Interfaces is relevant to geospatial formats, for example, in relation to support for interface services approved by the Open Geospatial Consortium [1].

The factors discussed below are specific to the geospatial nature of the resources and the desired functionality for geospatial use and analysis.

Normal GIS Functionality
Regardless of underlying content type (raster, vector, or attribute), the most fundamental capability for a geospatial format is georeferencing, placing information in relation to the surface of the earth using place names or assigning coordinates. To align different geospatial resources, they must all use or be transformed to the same geographic reference system, including what is known as a datum. If two resources use different known datums, a transformation of coordinates between the two systems can be made. For more information about terms such as georeferencing and datum, see Characteristics of Geospatial Formats. Any geospatial format must support declaration of the datum used for coordinate data within the resource. Projection (the conversion of the earth's curved surface onto a flat map) and scale (for images) must also be declared or understood implicitly to facilitate normal functioning. There are well known datums and projections that are in common use and given identifiers.

Normal functionality within a geographical information system (GIS) involves support for the basic spatial analysis functions described at GIS Functionality: Basic Spatial Analysis.

Some geospatial formats support more specialized spatial analyses. One example of more advanced functionality is the use of statistical techniques such as spatial interpolation and spatial prediction to provide additional data points when data is sparse or missing. See GIS Functionality: Spatial Interpolation and Estimation.

Support for GIS metadata
GIS metadata is an example of domain specific metadata and can be described as the degree to which a format can embed metadata using metadata models or standards developed by the geospatial community. In addition to the metadata needed to support normal functionality, assessment of a resource's fitness for a particular purpose requires information about the quality of the data and its provenance and lineage. See GIS Metadata and Data Documentation for more discussion on these topics.

The geospatial community has developed some community models and standards for metadata. These include ISO 19115 and standards from the Federal Geographic Data Committee (FGDC):

  • ISO 19115:2003 "defines the schema required for describing geographic information and services. It provides information about the identification, the extent, the quality, the spatial and temporal schema, spatial reference, and distribution of digital geographic data." This standard is being updated, with an expected publication date in 2013. [2]
  • ISO 19115-2:2009 "extends the existing geographic metadata standard by defining the schema required for describing imagery and gridded data. It provides information about the properties of the measuring equipment used to acquire the data, the geometry of the measuring process employed by the equipment, and the production process used to digitize the raw data. This extension deals with metadata needed to describe the derivation of geographic information from raw data, including the properties of the measuring system, and the numerical methods and computational procedures used in the derivation." [3]
  • FGDC Content Standard for Digital Geospatial Metadata (CSDGM), Published June 1994. Revised 1998. [4]
  • FGDC/INCITS North American Profile of ISO 19115:2003, Geographic information - Metadata. INCITS 453-2009. Intended to supersede CSDGM. [5]

Note: The compilers of this resource acknowledge that there is an overlap conceptually between this factor and the more generic Support for Data Documentation factor for dataset format. However, the particular importance of rich documentation for geospatial data resources appeared to warrant a factor that would appear in the geospatial section of format description documents.

Support for grid-based analysis
Grid-based analysis is a GIS functionality worth highlighting. The area of interest is divided into rectangular cells based on geo-location (using a known datum and projection). The cells contain data values from a variety of sources and are stored in a format designed to hold gridded data. The values are then available for various forms of spatial and statistical analysis. Grids contain information that can range from geographic coordinates to reflectance values from solar radiation hitting surface features. Since grid capability enhances the utility of geospatial data, format descriptions document when and how a format supports the use of gridded data. See Grid-based Analysis for more information.


1. Open Geospatial Consortium.

2. ISO 19115:2003. Geographic information - Metadata.

3. ISO 19115-2:2009 Geographic information -- Metadata -- Part 2: Extensions for imagery and gridded data.

4. FGDC Content Standard for Digital Geospatial Metadata (CSDGM), Published June 1994. Revised 1998.

5. FGDC/INCITS North American Profile of ISO 19115:2003, Geographic information - Metadata. ANSI/INCITS 453-2009. Intended to supersede CSDGM.

6. Draft North American Profile of ISO 19115:2003 - Geographic information - Metadata. Version 1.1, 2007-07-26. This draft, unlike the ISO and ANSI standards, which must be purchased, is publicly available.

This document, the companion Introduction to Geospatial Resources and Formats, and many of this Web site's geospatial format description pages were developed during 2010 and 2011 by Nancy Hoebelheinrich (Knowledge Motifs LLC) and Natalie Munn (Content Innovations LLC), based on work carried out by the National Geospatial Digital Archive and in cooperation with the Library of Congress format sustainability team and other specialists.

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Last Updated: 01/21/2022