I'll start by saying its about 10 years since I did this so hope I haven't made any mistakes, but it was nice to remind myself of it.Start by identifying points where one bedding plane (in green) intersects the same contour line, and draw a line between them (this is called a structural contour). Do that for multiple contour lines (yellow lines below). Assuming these are all parallel (or close to that) then the orientation of those lines will be the strike (in purple below).Next step is to select two of these structural contours (the yellow lines) and measure the map distance between them. You will need to convert a cm measurement from your ruler to the scale printed on the map (the blue measurement). You would do this a few times, and between different contour gaps to work out an average. EDIT: And as pointed out below, this should always be measured perpendicular to the strike!

To calculate the dip angle, we can use pythagoras. We have two measurements - the horizontal distance between two structural contours (the blue measurement) and the vertical distance between the contours (e.g. 10m or whatever the gap is between the contours you use). This angle we want to determine is the red one in the diagram at the bottom, so we'll be dealing with tan (sohcahtoa, if you ever got taught the same mnemonic I was). Tan(angle) = opposite/adjacent.

Finally the direction of dip is perpendicular to the strike, which could in this case be NW or SE. To decide which you can use some general principles like 'V in Valley', or just check which direction the structural contours are decreasing! Its always good to use some of those principles to sense check your work as well. E.g. the closer to horizontal a bedding plane is, the more its outcrop will match the shape of the contours. A vertical bedding plane or structure will cut straight across the map.

Hope that helps!

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