Page 120 - Statistics and Data Analysis in Geology

Chapter 5

Spatial Analysis

Although geologists study a three-dimensional world, their view of it is
strongly two dimensional. This reflects in part the fact that the third dimension,
depth, often is accessible to only a fraction of the extent of the other two spa-
tial dimensions. Also, our thoughts are conditioned by the media in which we
express them, and maps, photographs, and cross-sections are printed or drawn on
flat sheets of paper. We may be interested in the geologic features exposed in a deep
mine with successive levels, adits, and raises creating a complex three-dimensional
net, yet we must reduce this network to flat projections in order to express our
ideas concerning the relationships we see.

Geologic Maps, Conventional and Otherwise

Geologists are carefully trained to read, utilize, and create maps; probably no other
group of scientists is as adept at expressing and envisioning dimensional relation-
ships. Maps are compact and efficient means of expressing spatial relationships
and details-they are as important to Earth scientists as the conventions for scales
and notes are to the musician.
In this chapter, we will examine methods for analyzing features on what we
loosely define as “maps”: two-dimensional representations of areas. Usually the
area is geographical (a quadrangle, mining district, country, etc.) and the map is
a method for reducing very large-scale spatial relationships so they can be easily
perceived. However, the representation may equally well be a “map” of a thin sec-
tion or electron photomicrograph, where the relationships between features have
been enlarged so they become visible. Maps, in this general definition, include tra-
ditional geologic and topographic maps and also aerial photographs, mine plans,