Using GIS on Ometepe
Intro
| Research Questions | Preliminary
Analysis
The previous section illustrated the two different ways of understanding the Ometepe petroglyphs: as artistic motifs and as objects located in space. Because these two ways of understanding are very different, integrating them poses interesting challenges to the archaeologist.
1) Scale
One challenge in dealing with these data are the different scales and types of archaeological information recorded. The basic unit of analysis for rock art research is a single motif, which may be characterized by sub-categories such as anthropomorphic, zoomorphic, abstract curvilinear, or abstract rectilinear. This is basically an aesthetic category, not a spatial one. Spatial analysis on the level of motif becomes complicated because several motifs may exist on a single boulder, often overlapping each other. Because of this, divisions between panels are sometimes made for convenience in drawing (e.g. to fit the size of the measuring tape one is using) rather than because there is a clear break.
The next scalar level is the boulder itself, which may contain from one to eight of the above panels. Boulders are easier to categorize spatially, since they have physical and not aesthetic boundaries. Boulders are thus the most basic unit of presentation in ArcView, but at the same time they can hold several panels. They should perhaps be thought of as a container holding a number of panels and their motifs. Boulders are in turn contained within sites, a term that generally refers to a bounded group of archaeological artifacts or features.
2) Recording Methods
On Ometepe site definitions were reached through archaeological survey. Field teams spread out at ten meter intervals, and walk in the same direction. When rocks with petroglyphs are found, the boulders are tagged, and the area explored further – beyond the bounds of the original survey area – to determine the boundary of the petroglyph area. Ideally, site boundaries reflect where archaeological material stops. In practice, however, they sometimes represent the presence of impassable vegetation, where the vegetation was too thick or unpleasant (Ometepe has many thorny and stinging trees) for further progress.
Because tropical vegetation can grow ten feet in a single season, only recently- or regularily-cleared fields have proved practicable to survey. Therefore at lower elevations, where soils are better and forest clearance is more regular, site boundaries are more likely to reflect the extent of ancient human presence than at higher elevations, where there is more forest and underbrush. Compensating for this inevitable human error is difficult. One use of GIS is to determine whether patterns are the same or different at different elevations, so that field archaeologists can gain a sense of what types of variation produce different data.