At the regional scale, data on obsidian consumption patterns in the central and south-central Andes were gathered from the original sources cited in summaries principally by Burger, et al.(2002;2000), as well as some more recent contributions from other sources. Regional studies of obsidian distributions require incorporating spatial data from a variety of maps and records. The bulk of these data consist of site locations and other archaeological phenomena, and these data derive from studies between 1960 and 2000 where spatial data in the Andean countries was referenced to an older coordinate system based on the Provisional South American Datum of 1956 - La Canoa, (PSAD56). Currently, the governments of these Andean countries are shifting their cartographic divisions to a modern datum based on World Geodetic System 1984 (WGS84) or the related Sistema de Referencia Geocéntrico para las Américas 2000(SIRGAS 2000) (Fortes, et al. 2006), a new continental reference system for South America. The Upper Colca Project functioned entirely in WGS84 in order to be consistent with global data sets such as satellite imagery and other forms of spatial data that have recently become available. The datum change from PSAD56 to WGS84 results in an incompatibility between historic datasets and recent work, when obsidian artifacts from older collections are chemically provenienced and the precise spatial origin of these artifacts can be difficult to ascertain. Ultimately all of these sites should be revisited and mapped with GPS using a modern system such as WGS84, but in the meantime a relocation of these site positions and transformations of the historic geographical data are required.

Spatial data in Peru and Bolivia are almost universally rely on the 1956 La Canoa (Venezuela) datum based on the International 1924 ellipsoid known as Provisional South American Datum (PSAD56). If data from PSAD56 and WGS84 data are inadvertently combined, the resulting misalignment of map features in the Arequipa area is approximately 300 to 700 m.

Table 5-1.The two reference ellipsoids used in Peruvian and Bolivian cartography(NIMA 1977).

Three parameter metric transformations that can be applied to UTM coordinates in the central Andes are shown in Table 5-2.

Table 5-2. Three parameter cartographic transformations for UTM coordinates from PSAD 1956 (La Canoa) to WGS 1984 (Dana 1998;Mugnier 2006: 496;NIMA 1977).

By using the WGS 1984 datum, the geographical data collected in the course of the Upper Colca Project research registered properly with newer spatial data from a variety of institutions such as international, US government, and private remote sensing sources. These datasets include global topographic data like SRTM, satellite imagery and DEM sources like ASTER, and these data are also consistent with web products like Google Earth. Furthermore, WGS84 is the native coordinate system of the Global Positioning System and therefore the dGPS data acquired during fieldwork in the Upper Colca did not require an additional geographical transformation. The majority of maps in the region will be released in WGS84 or SIRGAS 2000 in the coming years.