HEXAGONAL MAPPING: A NEW AND VISUALLY APPEALING METHOD FOR REPRESENTING CAVE AND KARST FEATURES

Creating intuitive and useful karst maps for public consumption has long been a goal for state and federal agencies. The expansion of interest in karst has repeatedly demonstrated that statewide inventorying of karst features is an asset for many user groups, including developers, researchers, and municipalities. Moreover, karst terrain is increasingly set aside both for public recreation, as well as for scientific and natural preservation. As a complication, public awareness of karst resources must be managed in conjunction with sensitivity to abuse of the resources. All this feeds into a need to cartographically display karst resources over multiple scales in an accessible and responsible fashion for both the end-user and the resource.

Numerous and different approaches to representing karst terrain, particularly cave density, have been adopted over the years with varying degrees of success. This work introduces a new approach, dividing up a region into a hexagonal grid and representing increasing cave and sinkhole density as increasing color intensity within each hexagon. The hexagonal grid is also oriented to the UTM grid to ease geolocation. A hexagon area of 250 meters (approximately 800 feet) from edge to edge is chosen as a compromise between map detail and cave entrance confidentiality. Cave density is approximated by aggregating total known cave passage length within a single hex. In a similar fashion, sinkhole density is approximated by percent of the hexagon mapped as sinkholes.

Hexagons are an improvement over traditional squares in that the hexagon’s edges are more equidistant from the central point of the polygon than a square’s, making the distance in each polygon more intuitively uniform. By using hexagons as discrete shapes to illustrate karst density, a region is pixelated sufficiently to keep cave entrance data confidential (protecting the subterranean resource) while providing acceptable resolution for end users to make informed decisions on the local and county scale. Finally, the use of hexagons in this fashion is applicable beyond karst to other resources including, but not limited to, flood zones, landslide potential, mine subsidence as well as biological variables such as species distribution.