GPH 111
Lab E – Introduction to
Topographic Maps
Examples from the
Glendale Quadrangle, AZ
Some items in this slide show appear/advance automatically. However, in most
instances, you will perform the transitions between items and/or slides by hitting
your mouse, the spacebar, or the down arrow on your keyboard. When you see the
*, this is your signal to hit one of the aforementioned keys to proceed to the next
part of the lecture.*
Lynn Newman
Copyright 2006
The topographic map is a valuable tool for many users and it is important to
know how to read them. These maps show a tremendous amount of
information, both physical and cultural. Depending on the scale, we can see
individual houses, schools, small rivers, lakes, individual mountains, railroads,
mining activities, agricultural areas, urban areas, etc. We will take a brief
“tour” of the map to introduce you to the basic features common to all
topographic maps. Let’s start with the information found around the exterior of
the map and we’ll begin in the upper right corner…*
Then it says 7.5 minute series. This tells us that there are 7.5 degrees of
The map
Below
thetitle
titleisisfirst…Glendale
the state and county…*
Quadrangle*
latitude and 7.5 degrees of longitude shown on the map.*
Now, let’s look at the bottom of the map. Starting in the lower right corner…this
is the name of the map and the year in which the map was published.
The map was photorevised in 1982, meaning that the map was updated from its first
publication. All map features shown in purple represent those changes that took place
between 1957 and 1982. When you examine the map, you’ll be able to see that it
definitely needs to be revised again!*
Moving to the left, we see the outline of the state of Arizona with a small black
box inside.
This shows you the location of this Glendale map sheet relative to the rest of the
state. This illustration is especially helpful if the map you are using is from a part of
the country that you are unfamiliar with.*
This scale is read as: one inch on the map represents 24,000 inches on the surface of
the earth. You can use other units, for example, 1 cm on the map represents 24,000 cm
on the Earth’s surface. As you can see, a representative fraction is a dimensionless
quantity, meaning one unit of any type on the map represents 24,000 of the same units
on earth.*
The top scale is called a
representative fraction*
This area shows two types of scales. There are three graphical scales (mile,
feet, kilometer) and a scale called a representative fraction (e.g.,1:24000).
These are the graphical scales. They are in three different units of measure and you’ll
use the one appropriate for the questions you are answering. Examine the mile scale,
notice that the scale has ‘zero’ in the middle. This means that the full length of this scale
is 2 miles! Be careful. The kilometer scale is then 2 km in length and the foot scale
represents a distance of 8000’.*
Just below the scales you will find the information regarding the contour interval for the
map. The contours are the lines of constant elevation (like the isotherms and isobars
that we’ve done already this semester). They are shown as brown lines on the
topographic maps. The base value (datum) for these maps is sea level (zero foot
elevation).
This map has a contour interval of 5 feet, which means that there is a 5 foot elevation
difference between adjacent contours on the map. This can be a 5’ difference either up
or down in elevation and you will be able to determine this once you have learned to
read the contours and interpret the characteristics of the terrain (Lab F).*
There are three different types of contour lines:
Contour lines: thin brown lines, generally without elevation markings on them.
Index contours: thick brown lines with elevation values identifying them.
Hachured contours: thick or thin brown lines with tick marks towards the inside of the
closed contour. These indicate closed depressions. (Not shown here)
On this map we can see both the contour and index contour lines.
The thick index contours are every 5th line and have reference
elevations marked on them. The index contours also help to make
counting lines much easier since they stand out from the others.
Example, we see two index contours: 1100 and 1125. Given these
two values, we can calculate the contour interval for this map (25’
difference / 5 lines = 5’). Remember, the contour interval can be
read from the bottom of the map below the scales.*
In the lower left corner we have the text which provides us with information on
the techniques used to create the map, organization that produced it, and a key
to what some of the lines and shading colors/patterns mean.
Click when ready*
Let’s say that you need information from an adjacent map sheet, i.e., you need to
have the topographic information for the area to the NE of this Glendale map.
You are in luck since the names of the adjacent maps are printed on this map.
Let’s look at the NE corner of the map…
The three
locations
of the
names
the SWHills
corner,
SE corner,
name ovals
of theshow
map the
sheet
you would
need
is thefor“Union
Quadrangle”.
and bottom adjoining map sheets (Tolleson, Fowler, and Phoenix).*
There are adjoining maps for all four sides and the four corners. Let’s look at
the bottom of the map…*
Legend Information on Topographic Maps
This information can be found in the appendix of your textbook – Appendix II,
pages A-3 to A-7.
On these pages you will find information of what the various standard colors
mean, along with the various symbols used to distinguish map features and
landforms.
In terms of color:
Brown – contour lines and other topographic features
Blue – hydrographic features (water) or glaciers
Black – features constructed or designated by humans, such as
buildings, roads, boundary lines, and names
Green – vegetation areas such as woodlands, forests, orchards, and
vineyards
Red – important roads and lines of the public land survey system
Gray or red tint – urban areas
Purple – features added from aerial photos during map revision*
DETERMINING POSITION ON THE MAP
TWO BASIC TECHNIQUES
•Latitude and Longitude – we worked with this in lab C, and
studied it in the textbook as well as in the online topic module.
•The United States Public Land Survey (USPLS)
Let’s start with latitude and longitude on the topographic map…*
Latitude and Longitude
Latitude: These lines run east/west and are used to measure positions north or
south of the equator (0o). Remember that the lines are parallel to each other
hence they are also referred to as parallels. The values can be given with
degrees, minutes, and seconds, followed by the ‘N’ or ‘S’ indicator. Remember
that one degree is divided into 60 minutes (1o=60’) and each minute is divided
into 60 seconds (1’=60”). If you think of a degree as being an hour, then the
divisions seem logical. Latitude example: 34o50’12”N
Longitude: These lines run north/south and are used to measure positions
east or west of the Prime Meridian (0o). Remember that the Prime Meridian
runs from the north pole, through Greenwich, England to the south pole. These
lines are also referred to as meridians. These values are given in the same
format as latitude, but with a trailing ‘W’ or ‘E’ indicator. Longitude example:
129o23’06”W
*When giving coordinates for a location, latitude is written first, then longitude.*
Let’sprime
look across
therepresents
top of the zero
map.longitude
In each corner
we find
the to
latitude
and(right)
longitude
The
meridian
so it would
be far
the east
of
coordinateslocation.
for each Therefore,
corner location.
How doon
wethis
tell map
which
value
each pairinisthe
latitude
Glendale’s
all longitudes
(and
forofanywhere
and which
is longitude?
The red
lineofisthe
a line
of latitude,
that has a constant
United
States,
would be West
(west
prime
meridian).*
value. That is, as long as we are on this line, the value of latitude will not change,
hence, the value of 33o 37’ 30” which we see at both corners is the latitude.*
To England

Longitude changes as we move east or west and you can see that the other value in
each pair is changing. Notice that the value is increasing as we move west.* Values
increase from 07’30” to 15’ (reading right to left). Notice that this distance is 7.5o of
longitude. Are the longitudes East or West on this map sheet? To answer this,
ask yourself, “where would the prime meridian be located?”*
The red line shows a line of
longitude. Notice the value
of 112o07’30” is the same
at the top and bottom.
This is the longitude of this
line. Now latitude is
changing since we are
moving north and south on
the map. Values run from
33o30’ to 33o37’30” –
again 7.5 degrees. Now
you can see why the map
is called a 7.5 minute
series. It is 7.5’ in latitude
by 7.5’ in longitude.
You can see that latitude is
decreasing to the south
where at the equator it will
be zero. Therefore, all
latitudes on this map are
“north”.*
Besides the corners, you will find other values of latitude and longitude on the
map. These are located at about 1/3 and 2/3 the way across and down the map.
Other values in a different type face (font) are from a different coordinate system
that you are not responsible for knowing. On this map we have the following
values marked on the map for longitude…
112o15’
12’30”
10’
112o07’30”
These two values are shown on the map as written here. Notice that the degree
values are left off. This is done to save space. However, when you are giving
latitude or longitude for a place, be sure to put them back before giving your
answer!*
US Public Land Survey (USPLS)
The Public Land Survey System is a grid system linked to latitude and
longitude and employs a rectangular grid system. This system divides the
nation into a large number of standard sized units called townships and
sections. This pattern is quite evident in the street grid pattern of most U.S.
cities. Sites are located with reference to an east-west BASELINE and a northsouth PRINCIPAL MERIDIAN which are at right angles to each other. Both
lines, like latitude and longitude, run through an initial point. The initial survey
began in 1785 in the Ohio Valley. Arizona’s survey began in 1865 with the
initial point for the survey being the confluence of the Gila and Salt Rivers,
south of the Glendale campus near Avondale. The baseline for Arizona is
Baseline Road.
Once a principal meridian and baseline are drawn, a grid of lines, spaced at 6
mile intervals. The east-west lines in this grid form rows called townships. The
north-south lines form columns called ranges. The intersection of rows and
columns creates a pattern of boxes which are also (unfortunately) called
townships. Townships are divided into 36 smaller boxes (1 mile on a side).
These are called sections. Sections are numbered in a particular fashion, see
the pictures that follow to demonstrate the system.*
Notice how the grid is numbered. We count the number of boxes that we are
either east or west of the Principal Meridian and also how many north or south of
baseline. For example, see the yellow highlighed box. Click and watch the
numbering on the example below…the yellow township is 3 boxes to the east and 4
boxes to the north so we write Township 4 North, Range 3 East (T.4N., R.3E.).*
Each
township
is 6 miles
on a side.
4
6 miles
2
3
1
2
1
3
When demonstration is complete, click mouse twice**
Let’s take the highlighted township (yellow box) from the previous slide. This was
Township 4 North, Range 3 East (T.4N., R.3E.). This, and all townships are divided
into 36 sections and are numbered as shown in the upper left diagram. Section 1 is
always in the upper right increasing to the left, then we drop down a row and move
back to the right. This continues until we reach section 36 in the lower right.*
36 sections = 1 township
Each section is 1 mile on a side.
1 mile
Now, let’s zoom in on section
14 of T.4N., R.3E. We’ll focus
on the location where the star
is located.*
14
NW¼
NE¼
SW¼
SE¼
One square mile (size of section) is a large area so we subdivide a section first into
quarters, then smaller units as we’ll see shortly. First, we can see that the star is
located in the southwest ¼ of section 14. So at this point, the proper USPLS
designation for the star would be: SW¼, section 14, T.4N., R.3E. We can
subdivide the ¼ sections even further.* Now we can express the location of the
star as: NE¼, SW¼, section 14, T.4N., R.3E. You can subdivide even
further*…now the location is SE¼, NE¼, SW¼, section 14, T.4N., R.3E. You
can that the smaller the parcel of land you own, the longer the description is! This
is the method of location commonly used by real estate as well as many cities and
municipalities. We won’t go into that much detail in lab.*
Let’s see what this looks like on a topographic map…in this picture you can see
the division between range 1 east and range 2 east (R.1E., R.2E.). You’ll find
these divisions both along the top and bottom of the map (this is the bottom).
The township divisions are found along the sides (left and right) of the map.
Note the section numbers, 24 is the far right section of R.1E. And 19 is the far
left section of R.2E. See the diagram two slides earlier to see that this is true.
Note: the downward red arrow and the words Fowler 3.5 mi has nothing to do
with the public land survey so you may ignore it. It simply is telling you that if
you follow the road 3.5 miles south, you will get to the town named Fowler.*
Here you can see multiple sections and also the
township boundary on the left side separating T.2N.
From T.3N. This boundary is Northern Avenue. Note
that section 34 (in T.3N.) and section 3 (in T.2N.) are
not complete – we can’t see all of it. Therefore, the
townships that contain these sections are NOT
complete!*
Here is one more example: you can see the township and range separations clearly
here. Also notice that we are separating T.1N. and T.1S. – look at the name of the
dividing line…it is the Base Line. This map section comes from the Colorado River
at Parker, AZ.*
You are now finished with the lecture materials for Lab E – topographic maps.
You will have another exercise dealing with reading the terrain (contours) in a
couple of weeks. This is found in lab F.