Short history
A common practice when mapping large geographic areas was to divide an area into smaller sections, so that each one could be drafted in greater detail and printed on manageable sizes of physical paper. These sections making up a “map series” are extremely common in map collections containing maps from the 20th century, as war-time events created an effort to survey expanses of lands for military purposes, or as industrialization drove a desire to inventory natural resources.
Map series: several map sheets representing one body of work
An example of a map series is the International Map of the World (a.k.a. the “Millionth Map”, or the “IMW”). Starting in 1913, this was the first major international effort to map the entire earth at a consistent scale (1:1 million) and with standardized cartographic style. Before this map series, world maps only existed at scales of around 1:20 million or more, and on normal map-sized paper, this meant that details needed to be limited. The IMW essentially allowed the entire continuous world to be mapped in much greater detail. The map index for the IMW is defined by parallel lines of latitude and longitude, with each section being 4 degrees x 6 degrees. A cartesian-like system was created to identify each section according to its row and column above and below the equator, so that each section could be logically and uniquely named. In libraries, we still use this grid as an index to describe, find, and arrange IMW collections.
In libraries today
Index maps have been an important finding aid for map collections in libraries for the last several decades. These indexes act as spatial “table of contents” for the maps contained in a series of maps. They are important for users to determine which sheet covers a particular location–-information that cannot be adequately described in a traditional catalogue record.
Over time, libraries started using spatial technologies to extend discoverability of map collections. For instance, GeoBlacklight is a discovery interface for maps and geospatial data, which uses lat/long coordinates in a map’s descriptive metadata to reveal relevant resources when a user zooms a map to a particular location.
As map collections move online, the importance of index maps is even more apparent. In physical form, indexes are very often attached to, bound with, or in close proximity to the maps themselves. Online, disparate images of maps–often inadequately linked to adjacent sheets or the collection as a whole–are further removed from their index counterparts in a digital space. For map sheets in a map series with a large scale–lots of detail, but few familiar geographic features for reference–it is hard to determine the geographic location of the map. For example, unless you were from the few blocks displayed on this map in Vancouver, it is difficult to know where this map is showing, or even where to look to find out. <!– Some stuff about Open Index Maps and GeoBlacklight
- both for sharing holdings, and for spatial discoverability
- without GeoBlacklight, could use Mapbox GL JS –>
More information
- Clearinghouse of GIS indexes for paper map sets: This site, maintained by Christopher Thiry, Map Librarian at the Colorado School of Mines, serves as an open clearinghouse for GIS-produced indexes for paper map sets. The layer packages only contain base information about the paper maps, not information about a specific library’s holdings.
- OpenIndexMaps GitHub organization: Similar to the above clearinghouse, this GitHub organization serves as an open metadata collection of OpenIndexMaps GeoJSON files.
- Digital index maps: Leveraging GIS to create metadata for online map collections: This article, by Geospatial Data Curator Tom Brittnacher, explains how the University of California Santa Barbara Library sped up the metadata-creation process for map sets by using GIS software to create digital index maps. The article provides a conceptual overview of digital index maps, as well as important considerations for their creation.
- Creating GeoJSON files for OpenIndexMaps: This workshop, created by Cornell University GIS Librarian Keith Jenkins, demonstrates how to use QGIS to create OpenIndexMaps GeoJSON files that can be used in GeoBlacklight (GBL) to provide access to a series of maps or other datasets.