When you are using a protractor to measure the orientation of a line,
that means you're looking at a map. Notice the North arrow here -- that means it's a map.
So let's, for example, look at point A to point B. If I'm moving from point A to point B
on the map and I want to get the orientation, I want to get it from
North. Notice it's pointing towards the northern half of the map? So I'm going to -- before I
set my protractor down -- ask what zero is. If I'm going to measure the orientation, bearing,
heading of this from North then zero is North so I have to put the zero portion of my protractor
facing in the same direction as North. And of course the center is going to go over
point A. So it's going to look like this. Tt's facing North and so I am measuring the angle
to the right of North or to the East of North. And it ends up being 56 degrees plus or minus
1 degree. That is the oceanographer's method. A geologist would write that as north 56 degrees
east plus or minus one degree. Now let's look at this. This is the opposite direction,
so to get the correct orientation of this line, if I was a geologist,
I'd want to start by facing south. As an oceanographer I would still want to
start by facing north but I don't have a protractor that can go all the way around
to reach that arrow. It only goes to 180. This arrow is more than 180. For an oceanographer
so the best thing to do is to measure from south. So I'm going to flip this around so
my zero point south and I'll go ahead and stick my hole over the B line. In this case here's south,
so it's south 56 degrees south 56 degrees west plus or minus 1 degree because that's
that's the best I think I can get. If I move this around I'm not perfectly straight. It's going
to go up and down about a degree. How would an oceanographer say that? Well it'd be 180
plus 56. 180 plus 56 is 236 degrees plus or minus 1 degree. Notice that the oceanographer method has
no letter because you're starting from north and going clockwise.
You don't need -- it's always clockwise -- you don't need a letter to describe that.
The geologist method you have to actually bring in the starting point -- either north
or the or south -- and then how many degrees to the east or west you travel.
This last one is just for geologists. If I have a line on a page, which you're
going to see a lot in the geology lab, and there's no arrow facing either direction
then this could be north 56 east or it could be south 56 west and we don't like
to have two options. So we just pick north 56 degrees east plus or minus one degree.
Another thing you've learned about in this class is latitude and longitudes. Latitudes
and longitudes are coordinate systems they are not bearings. So this whole thing is about bearings,
headings, or what we also refer to as orientation of a line. In geology later you will talk about
dip and in dip we're looking at how rocks tilt relative to a horizontal surface. This is where
finding out what zero is supposed to be first is the way to ensure you use your protractor
correctly. Remember up here zero was north so we started by having our zero be north. Here the zero
was south so we started by having our zero point south. Here when we're dealing with how things dip
under a horizontal, zero is the horizontal so we take the bed, let's put a dot right there
where it intersects the horizontal, put that over our dot and now we're looking at the angle that
comes down under -- 0 being horizontal. So 0 to 30. So this would be a 30 degree dip. We will
get to dips later but I wanted to make sure you understand they have a different way of using
the protractor. Latitude, longitude, again, is a coordinate system so just a reminder that latitude
and longitude are just a spot you are on the planet and they have a format like 30
degrees north plus or minus 2 degrees and 120 degrees west plus or minus 2 degrees.
These are a coordinate system. They're very different. Notice the different format. It does
not match the format at all of an orientation. That makes it much easier -- we should be able
to recognize latitude and longitude when we see it because of those letters with the numbers and
recognize it's a completely different beast. Coordinate system and orientation of a line.