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.