Abstract: An Introduction to Gridding and Contouring Geologic Surfaces with a Computer

Mark A. Catanzano

Many geoscientists are now using inexpensive mapping programs and fast personal computers to create contour maps. Those geoscientists new to computer-assisted mapping often accept the program defaults and allow the program to control the mapping process. This paper provides inexperienced users with a basic understanding of what the mapping program is doing and how to include their geologic knowledge and expertise into the resulting map.

One of the most important aspects of computer-assisted mapping is an understanding and knowledge if gridding. Gridding is the conversion of irregularly-distributed data points into an ordered array(grid) of calculated values. The grid is what the mapping program uses to produce a contour ap. It is when the geoscientist is defining the grid, choosing the appropriate gridding algorithm, and selecting the gridding parameters that personal geologic expertise can be directly input into the mapping process. There are five main types of gridding algorithms: independent node, node spreading convergence, polygonal, curve fitting, and triangulation. Kriging can be viewed as a geostatistical version of the independent node type algorithm. Some general properties of grids and gridding parameters ill be illustrated with examples. In addition, opportunities for the geoscientist to provide geologic direction to the gridding algorithm and the data populations where the algorithm works most effectively will be considered for selected gridding algorithms.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas