Avoiding Pitfalls When Mapping with Personal Computers

Joseph E. Robinson, Paul D. Willette

The proliferation of inexpensive personal computers and user-friendly mapping software has helped geologists contour maps and apply trend analysis techniques to geologic data. Many of the current contouring programs designed for personal computers include both polynomial surface fitting and Fourier series trend analysis. These techniques are useful when correctly applied; however, with some programs relatively minor variations in the original input data can lead to serious distortions in the contoured results, creating anomalies where none exist. Most of the available mapping programs have some idiosyncrasies, yet can produce good results when judiciously applied to suitable data.

Problems may arise from the choice of contouring method, whether gridding or triangulation, and how it is applied to the original data. Contouring can also have a major effect on the presentation of the trend analysis results. The contour smoothing procedure is important and may be the determining factor in whether the completed maps are acceptable. Often the original data set must be modified before it is suitable for analysis. Data sets for polynomial trend analysis may require segmentation to produce valid results and Fourier analysis data usually require preprocessing and enlargement of the map area.

Processing problems are not restricted to personal computers and even occur with the most costly mainframe software systems. However, the more rigid requirements for small computer programs tend to restrict user choice to achieve processing speed and simplicity, sometimes at the expense of accuracy. Fortunately, relatively simple tests applied to known surface configurations expose any variations caused by the programs and permit the user to evaluate potential pitfalls in the application of mapping packages and to devise strategies to avoid errors.

AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.