Measuring the dip and strike of rock layers is a fundamental tool for understanding the three dimensional distribution of rocks within Earth's crust.

1. One way to think of the strike is it represents the compass direction (azimuth) of the trace of a layer across the surface of the Earth, if the surface is approximately horizontal. This means a measurement of the strike will tell you the direction a layer should appear on a geological map.
2. The dip is the angle of inclination of the layer with respect to the surface. This angle is measured perpendicular to the strike.

This web site from the University of Calgary gives a good visual summary of how to make these measurements.

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