Find Strike And Dip Given Structure Contour And One Other Point

To determine the dip of the bed, we need to draw a line through the additional point (P) and perpendicular to the structure contour. There are two ways of doing this:

1. Use a right angle like the corner of an index card or a draftsman's triangle to draw the perpendicular.

2. Use a compass:
-- Using point P as a center, draw an arc that cuts the structure contour in two places (A and A').
-- Using A and A' as centers, draw two intersecting arcs. A line from point P to this intersection (B) is the perpendicular.

1. Find the strike and dip of the limestone layer from the data at left.

2. Find the dip either by drawing a cross-section or by trigonometry.

3. With the dip known, find the map spacing between contours using either cross-section or trigonometry.

4. Construct other contours parallel to the known contour and with the correct spacing.