Maps are one of the best methods for answering the question “Where are we?” For centuries, accurate maps have been considered essential economic and military tools closely held and rarely available to the public. Until the 1960s, government maps often censored details of military bases. Maps are also useful for displaying the current, past, and expected future condition of a property. The anticipated uses of a map dictate its theme, scale, orientation, level of detail, and other features.
Maps are models of conditions on the ground. They
are used to orient oneself for travel and to communicate with others
about the physical setting. By convention, people have developed
standards for preparing maps that allow anyone, anyplace to
understand the geography and physical positioning of things in the
landscape. Some key characteristics of maps are:
Orientation: Early
maps were often oriented in relation to prominent landmarks, such as
mountains, rivers, or settlements. Over the years, the convention has
been adopted of orienting maps in relation to the earth's poles or
compass direction. Printed maps are usually turned north-south with
north being the top of the map. You should check the orientation of
the map you are using which is usually indicated by an arrow on the
map. If you are preparing a map for others, carefully consider before
orienting it in other than a north-south direction. The north-south
convention is so universal that exceptions to this rule often cause
confusion.
Scale: Scale is the
relationship between the distance measured on a map and the same
distance on the earth's surface. The scale of a map dictates how much
of the ground is illustrated, and the level of detail shown. As the
scale of a map gets larger, less area is shown, but in more detail.
Smaller scale maps show large areas in less detail.
Think about a typical road map that covers the
state of California. The small
scale map of the state shows the
interstate highways, state numbered highways, the names of cities and
towns, and symbols for attractions and destinations and county
boundaries. Large bodies of water, mountains, and state and national
parks and recreation areas might be shaded a different color. Such a
small scale map is useful for navigating from place to place across
hundreds of miles but is rarely useful for getting across town.
If you look in the margins of the state map, there
are usually details of major urban areas like the Bay Area, Los
Angeles, and Sacramento. These larger
scale regional maps present a smaller
amount of the ground but in much greater detail. More local roads and
destinations are presented. Still, if you are looking for a
particular address, you might need to get an even larger scale map
that shows even more detail like street names and numbers, city
limits, smaller parks, hospitals, and civic building like post
offices and libraries.
Each of these maps has a distinct scale, and each is useful for particular functions. There needs to be a balance between scale and the level of detail necessary to make the map useful. The state scale map helps you travel long distances efficiently. The regional scale maps show the details of the freeway system that help you find the right exit while not overwhelming you with detail. The street scale map helps find the exact address that you are looking for.
Every map should have its scale listed somewhere
in its margins. On highway maps, scale is often expressed with a
graphic ruler bar that shows how many miles on the ground are shown
by one inch on the map. The state map has a scale of 1 inch = 25
miles. The regional map has a scale of 1 inch = 10 miles, while the
city map shows 1/4 mile in each map inch.
Scale is often expressed as a ratio, such as 1:24,000, which means
that one map unit, such as an inch measured on the map, represents
24,000 of the same units, in this example inches, on the ground. Some
simple math is required to convert the ratio to a useful
relationship. Knowing that there are 12 inches in each foot, we can
calculate that each map inch represents 2,000 feet on the ground, a
very useful scale for land management.
Theme: Every map is
designed to display a particular set of conditions or its theme. This
theme dictates what details will be included and those that must be
ignored. Our road maps have a travel theme, helping you navigate from
place to place. The details that are presented, roads, city names,
parks, mountains, and water bodies are of interest to the traveling
public.
The US Geological Survey (USGS) publishes a set of maps that are very
useful for land management activities. USGS topographic maps, show
land form (hills and valleys), cultural features (roads and
buildings), and natural features (water and vegetation) using
standardized symbols.
USGS topographic maps make excellent base maps for other information that you are trying to display. Resource professionals are very familiar with USGS “topos.” It would be to your advantage to become familiar with using them.
A representative example USGS map appears in Figure 1. Since it is difficult to reproduce an entire topographic sheet that can be read in this small format, you may want to obtain a topographic map of your property to follow along.
Legend: Just about
every detail on a topographic map has a specific use and reason to
appear. First, scan the margins. In the lower right corner of the map
you will find its name, some location information, and the date that
the map was published. Each map is named for some local prominent
feature. The date tells you how recent the map is. Some information
will change over time, other items are unlikely to change very much
over time.
Above the map’s name is a brief legend that describes the road classifications. A more complete legend is available from the USGS.
To the left of the name and legend is a small
locator map that shows the approximate location of the topographic
map in the state.
Scale and Contour:
In the center of the lower margin is the scale, shown as a ratio
1:24,000 or each inch on the map represents 2,000 feet on the ground.
There is also a series of scale bars. The scale allows you to measure
distances and areas on the map. USGS topographic maps come in a
variety of scales, the most common that landowners will use are the
1:24,000 scale and the 1:62,500 scale.
Below the bars, the contour interval is given. In this case, it is 80 feet. One of the most obvious features on the topographic map are the curved brown lines that tend to parallel themselves. Each of these contour lines represents the same elevation along its course. That is, if you could follow a contour line exactly on the ground, you would stay at the same elevation, never going up or down. Contour lines are used to show the topography or shape of the land. The change in elevation between the lines, indicated by the contour interval is 80 feet. Within a set of contour lines, there can be small rises and depressions that do not exceed the 80 feet. Contour lines are chosen to match the topography of the map’s landscape. Contour lines never cross, nor do they cut across lakes.
The darker contour lines are index contours to help you quickly determine the elevation. Follow along one, and you will eventually be able to read the elevation of that index contour. Contour lines with a small dash perpendicular to the contour indicate a depression.
With a little practice, you can gain a great deal of skill reading contour lines. Lines that are close together show that the elevation changes rapidly in a short, horizontal distance, that is, the slope is steep. When the lines are farther apart, then the terrain is gently sloping. Figure 2 gives an example of how contour lines look on a map and on the ground.
Look along a blue line creek. The contour lines
tend to be V-shaped and point upstream. Contour lines that connect
and form a bulls-eye pattern, indicate the top of a hill. Skilled map
readers can infer a great deal about the underlying geology by the
shape an arrangement of contour lines.
Above the scale, in parenthesis, is the name of
the topographic map that borders the current sheet to the south. The
names of adjacent topos also appear in the the center of each side of
the map and an angle at the corners.
Declination: A
little to the left of the scale and contour interval along the bottom
of the map is the declination. USGS topos are oriented to true north.
Because a compass points to magnetic north, which in California is
about 17š (on this map 17 1/2š) east of true north, this difference
or declination is shown. Different parts of the state have slightly
different declinations. Declination also changes over time. Whenever
you use a map and compass together, you need to account for
declination. Better compasses have a declination adjustment
feature.
Marginal Notes: To
the left of the declination are notes that describe how the map was
made including details of the photographs used in mapping and field
work. This allows experienced users, surveyors, and others to compare
different map editions and measurements. For landowners, the most
significant notes are usually the dates that the aerial photography
was taken or when the map was updated.
Latitude and Longitude: Just above the marginal notes, at the corner of the map,
are two sets of numbers in degrees, minutes, seconds notation. On
this map they are 39o- 52´ 30” and 121´ 15”.
These indicate the latitude and longitude of the lower left hand
corner of the map. Latitude and longitude help place the details of
the map on the earth. They are usually expressed as degrees
(o) minutes
(´), and seconds (“). There are 60 seconds in each minute
and 60 minutes in each degree which makes the math somewhat
confusing.
Look at the bottom number, the longitude
121o 15´. Scan to the right most corner of the map
and find the corresponding longitude 121o 07´ 30”.
If you subtract one from the other, you get 7´ 30” or 7.5
minutes of longitude. If you look at the upper number
39o 52´ 30” the latitude, and then follow
up to the upper left hand corner of the map and read the
corresponding latitude at 40o 00´ 00”,
again the difference is 7.5 minutes.
Map Series: This is
how this map series gets its name 7.5 Minute Series noted in the
upper right hand corner. Each topographic map covers exactly 7.5
minutes of latitude and 7.5 minutes of longitude. An older, yet
popular series, covers 15 minutes of latitude and longitude or 4
– 7.5 minute maps, on each sheet. In the upper right corner, is
the name of the 15 minute map (NW 1/4 Bucks Lake 15´ Quadrangle)
that this topographic map was based on and which quarter – in
this case North West – of that 15 minute topographic map this
topographic map represents.
UTM Grid: The other
numbers equally spaced along the sides of the map with a smaller
number 44 followed by a number in a larger size type 16 give
coordinates in an alternative to latitude and longitude called
Universal Transverse Mercator or UTM. UTM is a grid system used to
plot your position on the Earth. It is mostly used in Geographic
Information Systems and military applications. UTM coordinates make
it easier to measure very long distances accurately.
Township and Range: The numbers in red along the sides in the form T 24 N and along the top and bottom in the form R 7 E give coordinates in the Public Land Survey. The Public Land Survey system in the U.S. is called the "township-range" system. Each 24 square mile area formed by intersecting latitude and longitude lines is broken into 16 township-range units which in turn are broken into 36 one-mile square sections. This system allows every part of the U.S. to have a uniquely defined location. Figure 3 shows how this works.
Legend: The meaning
of the symbols on a map are given in its legend. Every symbol, color,
and pattern have a specific meaning. Although any map may have its
own individual legend, USGS topological maps use a standard legend. A
pamphlet describing these symbols is available from the USGS.
Some symbols are colored on the maps. Water is shown as blue, vegetation is green. Roads and other works of humans are in black. Political divisions like the township and range lines are in red. Contour lines and topographic features are shown in brown. Recent changes are featured in purple. Dense urban areas are highlighted in a reddish tone that indicates some details are omitted.
Various agencies, organizations, and businesses
prepare numerous types of maps that can be useful. The county
assessor’s office has plat maps that show where your property is
in relation to your neighbors. The US Forest Service prepares maps of
national forests and the surrounding area that detail local road
networks and other features. The Natural Resource Conservation
Service distribute soil surveys with their associated map for many
counties. Most people carry a privately printed road map or two in
their vehicle. All of these are useful if you consider their scale,
orientation, and theme.
Other kinds of maps may be available at local or
federal government natural resource and planning departments. In
cases where local, state, or federal agencies have conducted studies
either on or near a person's property, the agency should be contacted
directly. Whenprocuring maps, it is important to determine when the
maps were prepared and by whom and what standards were used for
ensuring quality. This is particularly important when the maps have
been prepared by private companies either independently or for an
agency.
Maps are incredibly useful tools for describing
where activities occur. You should definitely have a copy of the
topographic map map that covers your property. You may want to order
a couple, one for a a clean office copy and another for the field. If
available, the soil survey information that covers your property will
help you plan management activities. The county plat map, shows your
boundaries and your neighbors. Note that plat maps show only rough
indications of boundaries, they are not surveys. Zoning maps from the
planning department indicate limitations that might apply to your
property.
You may also want maps prepared that describe your property in particular. A map of the road network showing gates, bridges, and culverts could be useful in planning and fire fighting. A map of the vegetation is a great planning tool. A map of the forest management history showing where and when units were harvested, planted, and otherwise treated provide a unique insight about your property. Often these are registered to a USGS topographic map.
Where you obtain maps depends on the type of map
you need. Once you have identified the publisher, be it a government
agency or private organization, the publisher of the map is usually
the best source of information on cost and availability. Local
libraries often have maps available for library use or loan. Most
universities and colleges have a map library that the public can
access.
The U.S. Geological Survey prepares topographic
and other types of maps for the U.S. USGS provides a free catalog of
the map products that they offer. If you can wait, ordering from the
USGS is the most cost-efficient means for obtaining a number of
useful map products. Contact information is at the end of this
leaflet. You can also purchase quadrangles at recreational supply
stores that serve campers, hikers, and hunters and sometimes at
stationary stores and small-town hardware stores.
Denver-ESIC
U.S. Geological Survey
Box 25286, Building 810
Denver Federal Center
Denver, CO 80225
Telephone: (303) 202-4200
FAX: (303) 202-4188
Email: infoservices@usgs.gov
USGS Information Services (Map and Book Sales)
Box 25286
Denver Federal Center
Denver, CO 80225
Telephone: (303) 202-4700 or 1-800-HELP-MAP
Fax: (303) 202-4693
Menlo Park-ESIC
U.S. Geological Survey
Building 3, MS 532, Rm. 3128
345 Middlefield Road
Menlo Park, CA 94025-3591
Telephone: (650) 329-4309
FAX: (650) 329-5130
TDD: (650) 329-5092
Email: esic_west@usgs.gov
1-800-USA-MAPS.
http://mapping.usgs.gov/
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Publication of this series was in part funded by the
California Department of Forestry and Fire Protection
under Contract numbers 8CA96027 and 8CA96028