1. Tracing Contacts Complex map patterns are due to
Messy geology
Convoluted intersection of geologic structures with the ground surface
Even simple geology can look complex because of topography.
Need to visualize intersection geometry to map and interpret geology correctly.

2. Tracing Contacts
If a unit is planar and we know the strike-and-dip at one location, we can trace the contact on the map…
Draw a cross-section perpendicular to strike (in the dip direction) through the outcrop point.
Project structure contours from the cross-section across the map topographic contours.
Draw contact following the resulting points of intersection between corresponding structure and topographic contours.