Planetary Map Data Model for Geologic Mapping

Article excerpt

Introduction

In the context of planetary exploration and systematic planetary mapping an increasing number of planetary maps have been created through agency-funded programs via individual or collaborative research projects. In order to be able to manage and prepare data for analysis and mapping, we are developing a geologic map data model. This model is composed of several modules and interfaces that enable integration of heterogeneous pieces of information derived from different sources. The low-level goal of such a research data model was to provide a common platform for integrating different sorts of geologic maps made in the context of different planetary research and mapping programs (van Gasselt and Nass 2010a,b; Nass et al. 2010). Modules and interfaces have been developed, expanded and tested separately, and together after integration into the overarching framework. One of the most complex modules deals with the storage and administration of geologic map-units within their regional to global planetary stratigraphy, as well as rock types that comprise these units. The rock composition forms boundaries that require effective symbology standardized by the Federal Geographic Data Committee.

Major aim of this work is to highlight some aspects of the capability of the planetary map data model (PMDM) in dealing with these requirements. Although a small number of different geologic data models have been conceptually developed, the PMDM follows a number of different approaches in order to handle in principle any planetary body with its very own individual stratigraphic systematics, and its own geologic record.

Principal application of this data model is demonstrated by a mapping project related to the landing sites of the manned Apollo missions in the early 1970s. These projects have been chosen as they provide a large data basis from high-resolution remote sensing as well as in-situ analysis. Additionally, the landing-site stratigraphy is determined through sample returns as well as techniques of remotely sensed impact crater size frequency measurements. Both techniques and results need to be modeled appropriately within the PMDM.

Geologic Mapping in General

Geologic maps are two-dimensional representations of a three-dimensional world made of a number of rock units deposited through time and stacked on top of each other. Each layer of rock material has been emplaced and formed during a discrete time span and a discrete process (Wilhelms 1990). Apart from information on the lateral distribution of geologic units within their geospatial context, there is information on the timing of rock-unit formation and deposition, such as information on the vertical distribution of rock material. The vertical distribution of rock units translates to time, either on a relative scale where oldest units are superimposed by younger units, or on an absolute scale based on direct measurements of rock samples using for example radioisotope decay. Such a vertical rock column is part of the stratigraphy, which establishes a local, regional and global context for representing rock units deposited trough time. For a discussion on the components of a geologic map from the technical viewpoint see Johnson et al. (1999).

Geologic maps are designed not only to show a representation of the lateral distribution of distinct units on a map sheet but also to provide additional information on the stratigraphy. Such information is usually placed as a stratigraphic column on the mapsheet legend that relates stratigraphic time-units and names of the units on the actual map by different colors and symbols.

Storage of geometry information and additional attribute values for each mapped unit are easily handled today by employing GIS. The integration of additional dimensions, such as the vertical stack of geologic materials and the stratigraphic context put higher demands on GIS environments. Efficient treatment of such spatial complexity requires the design of geospatial data models. …