Introduction to Topographic Maps

SPEAKER: Hi everybody!

Today we're going to take a look at
topographic maps, and I'm going to

teach you how to read them, and we're
going to go through some of the rules

that will help them make sense.

So right now you're looking at a
topographic map, and it probably

looks like a bunch of squiggles and
lines and colours.

Probably does not make too much sense
to you.

Here's another topographic map, the same
thing, probably just looks like a bunch of

brown squiggles with some other colours
thrown in there.

By the end of the video, hopefully you're
going to be able to look at a map like this

and you're going to be able to see the
topography, or the shape of the land.

So a topographic map looks like this one
on the bottom, and basically what they do

is they are a map that is able to show us
the elevation, the height above sea level,

and the shape of the land by using these
lines, which are a kind of isoline,

called contour lines.

So on the top we have a landscape, you
can see there's a cliff over here, there's

a hill over here.

When you know how to read a topographic
map you can actually look at this and

you can tell that there's a cliff over
here and there's a hill over here.

Topographic maps have certain features
that you will always see, so let's go

through 4 of those features.

The first thing you're going to have to
figure out is what the contour interval is.

When you look at a topographic map, you'll
notice that not every line is labelled.

For example, this map, we have 300
labeled, we have 400 labeled.

Those lines are a little bit darker than
the surrounding lines.

Those numbered lines are called index
contour lines, the reason they only

label some of them is because we don't
want the map to be too confusing,

we don't want numbers everywhere.

So, the first thing you have to do is
figure out what the contour interval is.

In other words, what is the difference
between each pair of lines?

Now, sometimes they'll tell you the
interval in a key under the map, but

more often than not you're gonna have to
determine it yourself.

So if we start with this map over here,
again we have 300 and it's

either meters or feet or kilometers,
we're not sure with this map because it

doesn't tell us.

But we have 300 here, we have 400 here.

So our task is to figure out what the
contour interval is, what are we gonna

count by to get to 300 to 400?

Now, hopefully, you're looking at this
and you're realizing, well, it's a

difference of 100 and it's spread out
over 5 lines, so 100 divided by 5

is 20.

So for this map the contour interval
would be 20 units.

So by units, we mean either miles or
kilometers or meters.

Let's take a look at this top left map
over here.

So we're going from 10, and then we're
skipping a line, it's not labeled, then

we're going to 20.

So that one's pretty easy, we're
counting by 5's.

The bottom left map over here, okay, I
see that this contour line is labeled

as 50, and this contour line up here is
labeled as 100.

So, again, it goes from 50 to 100, which
is a difference of 50, and it's going

5 lines between them, so 50 divided by
5 is 10.

And then on the last map, this one's
pretty easy to figure out.

We're counting by 25's, so our contour
interval would be 25 whatever unit is

being used.

Let's take a look at another map.

Can you figure out on this map what
the contour interval would be?

And feel free to pause the video.

Well hopefully you realized that we're
going from 500 to 600, so we're going

a difference of 100, and again we're
spreading it out over 5 lines so we're

counting with an interval of 20 meters.

Once you know the interval, you can now
figure out the elevation of any of the

lines that are not labeled.

So, for example, line A, right over
here, if we're counting by 20's, this

line would be 540 meters.

I want you to see if you could figure out
what the elevation of line B would be.

So think about that for a second.

And hopefully, you're realizing that
it's 580 meters.

Okay, so again: contour interval, first
thing you want to figure out.

The next thing that you'll notice on
most maps is somewhere there will be a

compass rose, and that's important
because that will show you where North is.

And normally when we look at a map, North
is usually up, but that is not always

the case.

You can see on this map that they're
telling you that north is facing the right

side of the map, so North is really here
and then South would be over here.

So you want to look at the compass rose,
you want to figure out where North is,

where South is.

So, let's go through some of the rules of
how to read a topographic map, okay.

Going back to this first map that we
looked at earlier.

I want you to notice when there's a cliff,
what the contour lines look like.

So right over here, where the land is
steep, you probably notice that the

contour lines are very close together,
and that's always going to be the case.

Rule #1 is the closer the lines are, the
steeper the slope.

Or, the opposite, the more spread out
the lines are, the gentler the slope.

We can see on the side of this hill over
here we have a nice flat area, uh,

right over here, the land is pretty flat
over here and on our contour map we can

see the lines are spread apart much
further than they were over there.

Now, on the back of your note sheet
you have this map.

I want you to go ahead and I want you
to figure out where the steepest

slope would be on this landscape.

So we're looking for where the lines are
the closest.

And pretty easy to see, the lines are the
closest somewhere near the top over here,

okay, you can see how close together
they are.

Go ahead and label that on your map,
on the back of your note sheet, that is

the steepest slope.

Okay, rule #2 deals with streams and
rivers: when a contour line crosses a

river or a stream, the contour line
bends and forms a V.

We can see that, again this is the map on
the back of your sheet, we have this

middle river over here, and we can
see that, when the contour lines cross

the river, they are bending and they are
forming V's.

You always want to look for the V's
because the V's will tell you where the

water is coming from.

So the tip of the V shows you the
source of the water.

So, in this case, the water is coming from
over here, this would be the source.

And so the water is travelling from this
bottom edge of the map, the river is

flowing this way towards the ocean.

and it eventually goes into the ocean,
and that would be called the mouth

of the stream, or the mouth of the river.

Let's practice that skill a little bit,
that's an important skill.

Let's take a look at this map, I want you
to see if you can figure out which way

Long Creek would be flowing.

Alright, so hopefully you noticed the
contour lines are bending, they're forming

V's, and again the tip of the V shows us
the source of the water, so Long Creek is

basically flowing towards the South,
slightly West, so South-West or South.

Here's another one, let's look at
Trout Stream over here.

See if you can figure out which way Trout
Stream would be flowing.

Alright, again, we look at our contour
lines, they are bending, they are forming

V's, the tip of the V shows us the source
of the stream, so the water is coming

from here and it is flowing down this
hill into the river.

We can see the same thing when we look at
the river.

If we look at Cedar River we have this
one contour line here that forms a V,

so we know the river is flowing this
direction towards the lake.

Okay, so that's how we figure out which
way streams and rivers are flowing.

Rule #3, you'll notice this landform over
here has 2 hills, when they are put on

a topographic map, they look like
concentric circles that get smaller

and smaller inside of each other.

Rule #3 is that when there are rings of
circles that get smaller and smaller, that

it represents a hill or a mountain.

So let's look at the map, again, that's
on the back of your sheet.

Let's figure out how many hills there are.

So, I see one over here, so let's go ahead
let's label that somewhere, if I click-

there we go!

So there's a hill, can you find any
others?

Well, you should, there are 2 others.

We have one hill over here where there are
circles inside of circles.

We have another one over here.

This area down here on the bottom
right-hand corner is not a hill because it

has these little marks on it, which we'll
get to in a couple of minutes.

Okay, so again, anytime you see circles
within circles, it is a hill or a mountain.

Now, what we have to do is we have to be
able to figure out how high the top of the

hill or the mountain is.

So to do that, what we would do, is we
would look at our map and we'd figure

out what our contour interval was.

Now, we looked at this one before.

So we know that this one is counting by
20's.

This top contour line is 400, which
means the top of the hill has to be

higher than 400, but it's not going to
be as high as what the next line would be.

So the next line, if there was one, would
be 420.

So the top of this hill is somewhere between
401 and 419 meters, or whatever unit it is.

So again, it can't be 400 and it can't be
420, it's gotta be in between.

How about on this map?

Again, we're counting by 20's, so if this
top line is 600 it means the top of the

hill has to be somewhere above that, but
lower than what the next line would be.

So it's got to be somewhere between 601
and 619, okay.

So rule #4 says: the highest possible
elevation of a hill is just below the value

of whatever the next contour line would
be, if there was a next contour line.

So let's figure out what the height of
these hills, okay.

So let's start with this one over here.

So this contour line is 300, so let's
figure out what we're counting by.

So here's 200, here's 300, so we're
counting by 20's.

So if we come up the hill, so this is 300,
320, 340, 360, 380.

So this small loop is 380, which means the
top of the hill has to be somewhere

between 381 and 399, it can't be 400
because if it was 400 we'd have another

line there, so the highest it could possibly
be is 399 meters.

If we take a look at this hill we could
figure out the same thing, we could

figure out the same thing down here.

So, in this case, here's 200, so the
circle where letter Z is, that's 220.

The next line would be 240, so the
elevation cant be that high it's got to

be underneath that. So the highest
would be 239.

Alright, moving on, rule #5, sometimes
we don't have a hill, sometimes the land

dips down and forms a depression.

So this is the top of a volcano, and
there's a crater up here, that's a

depression, on a contour map we show
depressions by using these little marks

that are called hachures or hatch marks.

So, again, we'd find these where there's a
volcanic crater, or maybe where a meteor

hit the Earth and left a crater.

So on your map, we see that right over
here we have a depression, so these

little hatcher marks tell us that the land
is going downwards, okay.

Now the last rule, the 6th rule, tells us
how we would figure out how deep the

bottom of the depression is, okay.

So the first part of the rules says
that when you at a depression,

the first hachured line,
so the outer circle,

has the same elevation
as the previous contour line.

So in other words,
this line over here

has an elevation of 120 meters.

So our first line with the
hatcher marks is also 120 meters.

Then what we do is we
start to go downwards.

So if this is 120,
it means the next line

is going down by 20.

So it is going to be 100.

To figure out the deepest that this
depression could be,

what we will do is --
we say 'if there was

another line, what would that be?'

So if there was another line
it would be 80.

But that line is not there.

So this depression can't go down to 80.

So it has got to be a little
bit higher than 80.

So the lowest possible elevation
is just above whatever the next

contour line would be.

Alright, so here is another
contour map.

Hopefully you can use
some of the rules we

went over and you can
figure out some of the topography.

Some of the shape of the landscape.

We are going to be doing
a lot of this in class.

Have fun!