a

Introduction to Topographic Maps

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 colors it

probably does not make too much sense to

you

here's another topographic map same

thing probably just looks like a bunch

of brown squiggles with some other

colors 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 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 ISO line

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 four 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 labeled 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 to have

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 going to have to

determine it yourself so if we start

with this map over here again we have

three

hundred 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 going to count

by to get from 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 five lines so

100 divided by five 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 a

hundred so again it goes from 50 to 100

which is a difference of 50 and it's

going five 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 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 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

five 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 20s 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 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 number one 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 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 number two deals with streams

and rivers when a contour line crosses a

river or a stream the contour line bends

and forms of V we can see that again

this is the map on the back of your

sheet we have this Miller 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 traveling from this bottom edge

of the map okay 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 all right so hopefully you

notice 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're forming

vias 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 going rule number three you'll

notice this land form over here has two

hills when they are put on a topographic

map

they look like concentric circles that

get smaller and smaller inside of each

other rule number three is that when

there are rings of circles that gets

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 and

somewhere if I click there we go so

there's a hill can you find any others

well you should there are two 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's counting by 20s

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 got to be in

between how about on this map well again

we're counting by 20s 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 number four 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 20s 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 okay 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 can't be that high it's

got to be underneath that so the highest

would be 239 all right moving on rule

number five 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

oppression on a contour map we show

depressions by using these little marks

that are called Hatcher's or hatch marks

so again we'd find these where there's a

volcanic crater or maybe a meteor hit

the earth and left the 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

sixth rule tells us how we would figure

out how deep the bottom of the

depression is okay so the first part of

the rule says that when you're at a

depression the first Hatcher Deline 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 a

hundred and twenty 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's going to be a

hundred to figure out the deepest that

this depression could be what we do is

we say all right 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's

got to be a little bit higher than 80 so

the lowest possible elevation is just

above whatever the next contour line

would be all right so here's another

contour map hopefully you can use some

of the rules who went over and you can

figure out some of the topography some

of the shape of the landscape we're

going to be doing a lot of this in class

have fun