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 made it easy for geologists to contour maps
and apply trend
analysis techniques to geologic data. Many of the current contouring programs
designed for use on personal computers include both polynomial surface fitting
and Fourier series trend analysis. These techniques are useful when correctly
applied. With some programs, however, relatively minor variations in the
original input data can lead to serious distortions in the contoured results,
thus creating anomalies where none exist. Most mapping programs have some
idiosyncrasies yet can produce good results when applied to suitable data.
Problems may arise from the choice of surface-fitting 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 a
data 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 in order
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 programs. They 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 #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.