A site is identified and two low-density loci and one medium and one high density lithic loci are identified and mapped. The medium and high density loci are, by definition, inside one of the low-density loci in a layer-cake fashion. Additionally, as described above a 100% collection of two or more sample units (1m²) per high density locus was conducted. Thus, returning from the field data consist of

(1) A site boundary polygon, two low-density polygons, and a medium and high density polygon mapped and attributed according to Attribute Category 1 (C1) and Attribute Category 2 (C2) variability (see Section 5.5.6"Variability within a Locus").

(2) Representative surface collections from the site and from each of the loci were gathered by fieldworkers with common knowledge of the description being entered into Arcpad as attributes by the mobile GIS user.

(3) A minimum of two 100% collection units from each high density locus were gathered.

These sources of data were combined, when available, to produce an "obsidian" and a "non-obsidian" lithics density raster surface. When a locus has a C1 of Obsidian and a C2 of Chert (for example), the Estimated Percentage for C1 and for C2 of that locus could be used to estimate the density for each cell of the GRID, scaling the representation of C1 and C2 by the percentages of each returned to the lab.

However, if a locus has a C1 of Obsidian, big flakes and a C2 of Obsidian, smaller flakes (same material, different sizes), for example, the lab results can be examined to see if there are non-obsidian artifacts collected for that locus. If so, then the count of those non-obsidian artifacts, as a percentage of the count of the whole collection, is assumed to represent the percentage of, say, quartzite in that locus that was predominantly obsidian based on its description. In that way, the weight and percentage of a given material type from lab analysis was used to calibrate field recordings of artifact scatter composition.

Using the locus definition rules stated above (i.e., high density locus = 10+ artifacts /m²) the polygons were converted to rasters and the following values were placed in the cells. The vector to raster conversion and the attenuation on the edges of each class were resolved by the mosaic command which averages the differences between raster surfaces along the contact boundaries between classes.

Table 5-11. Loci to GRID conversion values.

The Density value therefore ranks the polygons by their number of flakes per meter for variability in either Material Type, Reduction Level or Flake Size, and the raster creation focused on material type differences, but rasters could have been created, theoretically for the other characteristics as well.