B. Survey Systems
A related topic to coordinate systems is how we describe the
boundaries of parcels of land. SPC or UTM coordinates are great
for giving locations of points, but less so for describing area.
You can describe a parcel by going from point to point--this is
the first method below. But other methods are easier in some
circumstances. This section covers land-description methods used
in the US. An important fact about survey systems is that once
land is surveyed under a given system, that's it--the description
of the land stays with it permanently. Land within old Spanish
Land Grants in California still retain their descriptions based on
the original survey.
1. Metes-and-Bounds
Early settlers in the Thirteen Colonies used the same method
for dividing and describing land as they had in the Old World
(especially England). This system is known as metes-and-bounds.
The idea is very simple: a land parcel is described based on going
from one point to another, in a polygon that encompasses the
parcel. For example, a legal description might read:
"Commencing from a point one-half mile upstream from Smith
Bridge on Jones Creek, proceed northeast 500 feet to Spring Hill,
then northwest to the large oak tree, then southwest to the large
rock in the middle of Jones Creek, then along Jones Creek to the
origin."
The first settlers in an area naturally claimed the best land,
and set up boundaries that encompassed that land. Most of the
time, this worked alright, and in a sense it shapes human use of
the land according to the landscape itself, rather than imposing
an artificial pattern on the land.
But metes-and-bounds surveys are liable to create problems.
Since surveys were done as land was claimed, overlapping claims
often resulted--with lengthy court battles ensuing. Even today,
land titles are more difficult to verify in areas surveyed by
metes-&-bounds. A bigger problem is that the boundary markers
(oak tree, big rock) eventually are obliterated, with the
boundaries becoming ambiguous. One measure to help has been to
replace landmarks with exact compass directions and distances
(also known as "Coordinate Geometry"). The description above might
be replaced with:
"Commencing from a point one-half mile upstream from Smith
Bridge on Jones Creek, proceed N 45° E 500 feet, then N
50° W 324 feet, then S 35° W to Jones Creek, then along
Jones Creek to the origin."
A final problem with metes-&-bounds was that the US
government wanted to sell off land in the West quickly, in order
to raise cash (no income taxes back then). A system was needed
that could quickly and rationally divide up the land, allowing for
sales without a lot of legal wrangling. The US Public Land Survey,
described below, became the US answer to the problem.
2. Spanish Land Grants
The Spanish, and later Mexicans, ruled California and much of
the Southwest for about 300 years. They too parceled out land for
use by colonists (with little regard to Native occupation, of
course). The methods of description were very similar to
metes-and-bounds. Much of the land was given or sold to large
landowners for ranchos as Spanish Land Grants. These land grants
usually focused on water resources, which are scarce in the West;
sometimes the system is called Spanish Riparian (riparian means
relating to watercourses).
Much of the better land in California ended up in one of these
land grants. Remember, once allocated, land continues to be
described under its original survey, permanently. Even after
California became part of the US, and land grant claims were
honored (though sometimes exchanging hands under questionable
deals). The land grants have be subdivided since then, but
evidence still can be found in property descriptions, and on USGS
topographic maps. For instance, some land grants in Sonoma County
were Rancho Cabeza de Santa Rosa, Petaluma Rancho, and Rancho
Cotate. These labels, along with their boundaries, can be found on
topos for Sonoma County.
3. Other Irregular Surveys
Other survey methods were used in certain parts of the US. In
Louisiana and other areas settled by the French, long-lots were
used. The land along important lanes of commerce, usually rivers,
was divided into narrow strips extending back into the interior.
This resulted in a series of long but narrow plots of land that
are still evident on topo sheets of Louisiana, coastal Texas, and
Mississippi River towns, even as far upstream as Wisconsin.
4. The US Public Land Survey (PLS)
The majority of the land in the US is described under the US
Public Land Survey (PLS) System. After independence, the US wanted
to dispose quickly of lands in the West (at that time, land
between the 13 Colonies and the Mississippi River). Some form of
logical, orderly system was inevitable, but the exact form took
time to shape. Thomas Jefferson and others eventually worked out a
rational, rectangular (squarish) survey, called the Public Land
Survey (PLS) system, which was enacted under the Northwest Land
Ordinance of 1785 (with later revisions).
The PLS starts out by establishing an x,y coordinate system for
a given area. The north-south line is called a principal meridian,
and the east-west line a baseline. Each baseline is given a unique
name, so that each land parcel can be identified by that name. The
area described based on a principal meridian/baseline pair varies
from a small part of a state (e.g., eastern Ohio, northwestern
California), to several states (e.g., the Fifth Principal Meridian
covers most of Arkansas, Missouri, Iowa, Minnesota, and most of
the Dakotas).
California has three principal meridian/baseline pairs: the San
Bernardino Meridian (southern California), Mt. Diablo Meridian
(most of northern California), and the Humboldt Meridian
(northwestern corner of the state).
The initial point is the intersection of the principal meridian
and baseline. From this point, townships are marked off east/west
and north/south. Each township is 6 miles on a side, or 36 square
miles. Townships are designated on the east-west direction as
being a certain number of Ranges east or west of the principal
meridian. The township is also a certain number of Townships north
or south of the baseline (note the dual use of the term township,
as an area and as a coordinate). For example, the township that is
just on the northeast corner of the initial point is Township 1
North, Range 1 East, usually abbreviated T. 1 N, R. 1 E. Or T. 3
S, R. 2 W would be the third township south of the baseline and
two townships to the west.
Each township had to be divided, since few people could afford
36 mi2. The division was into 36 sections, one square mile each.
Rather than using an x,y system here, the sections were simply
numbered consecutively from 1 to 36, starting in the northeast
corner and snaking around the rows, with 36 at the southeast
corner.
Most land purchases were for less than one section; the
Homestead Act of 1863 allowed people to receive one-quarter
section if lived on by the claimant. Sections can be broken down
into halves or quarters, each part designated by a compass
direction. If divided in half, we have either east/west halves, or
north/south halves. If divided into quarters, we have the NE, NW,
SW, and SE quarters. Quarters can be broken down further if
necessary, for example we might have the NE quarter of the SE
quarter.
A square mile contains 640 acres, so a quarter section has 160
acres, a quarter-quarter 40 acres, and so on. The typical
Midwestern farm used to be a quarter section, or 160 acres. Farms
have been consolidated over the past several decades, so the
typical farm occupies closer to a square mile, especially in
California.
A complete property description must include all of these
breakdowns into township, section, and fraction of section (if
less than an entire section). A typical property description in a
PLS area might read:
NE 1/2 of SE 1/4, Sect. 22, T. 87 N, R. 34 E, 6th
Principal Meridian
USGS topographic maps indicate PLS townships and ranges along
the margins. Section and township lines are shown on the map
itself with red lines, and sections are numbered in red. You will
no doubt notice on some topos that the PLS townships and sections
end abruptly in some part of the map. This is common around Santa
Rosa. This is because these non-PLS lands were in Land Grants
before 1846, when California became part of the US. Remember, once
surveyed, never again.
The PLS has had a dramatic impact on the American landscape.
Since all land is divided into squares, the landscape itself looks
very square. You'll notice this when flying over the middle part
of the US, where topography does not interfere with its effects as
much. It also contributed to the isolation of farm families in the
19th Century, who lived on their own square farms far from
neighbors. Contrast this to French surveyed-lands, where people
live much closer together. Our survey system no doubt contributed
to the ideal of American individualism.
A final note about the PLS--it's far from a perfect system.
There are many irregularities, which are especially noticeable in
certain regions. Section and township lines are not always exactly
north/south and east/west, and sections are sometimes less than a
full square mile (they're then called government lots, or
fractional lots). The irregularities derive from several
sources:
- Meridians converge to the north, so as surveyors moved
north, townships didn't match up with those further south.
Often east-west correction lines were set up, along which
townships were re-aligned. You'll notice this effect when
driving north or south along a country road and you have to
take a sudden turn right or left, then turn north/south
again after a short distance.
- Surveying in wet or mountainous terrain is difficult,
and lines often went astray. Once set up, however, the
errors were kept, and lines remained askew.
- Surveyors were paid by the number of sections surveyed,
so hurried surveyors weren't always careful surveyors.
- Some surveyors simply weren't careful, or were even
staggering-drunk on the job.
Because of these irregularities, the PLS is not a great system
for computerized map coordinates when you want a regular x,y grid.
Use the UTM or SPC grid instead.
5. Other Rectangular Surveys
Some states weren't touched at all by the PLS: the original 13
Colonies (and subsequent split-offs: West Virginia, Vermont,
Maine), Tennessee, Kentucky, and Texas. Some New England towns
used a modified rectangular survey when settled. Some of the
states had considerable land left to dispose of in the 19th
Century, and developed their own rectangular survey for these
lands. Texas, in particular, used several variations on a
rectangular survey, some of which used Spanish units. These
rectangularly-surveyed areas look like PLS areas as you travel
over them, even though officially they're not.
Everything up to now can be applied to topographic maps
as well as other kinds of maps and information. The rest of this
discussion focuses specifically on how you can use topographic
maps to extract information about the landscape. Both physical and
cultural features are often discernible from topographic maps.
This section draws many ideas from a course handbook titled "The
Language of Maps," by my advisor at the University of Minnesota,
Phil Gersmehl.
The US Geological Survey has published many different kinds of
maps, including several series of topographic maps. Only a few
series are in common use. The 7 1/2-minute quadrangles, which have
a scale of 1:24,000, are the most popular. These detailed maps are
supplemented by the 1:250,000-scale series. A third series, the
15-minute quad at 1:62,500, was popular but discontinued by the
USGS for mysterious reasons (probably because the detailed
1:24,000 maps had to be done, and the 1:62,500s would duplicate
some of their uses). The 1:100,000-scale metric series is a recent
addition, and is now complete for the US. All of its maps show
features in metric, for example elevation is in meters.
A. Physical Features
In addition to this section, see also the discussion of contour
lines and slopes above under Symbolization in Part I. You may also
want to read (or reread) a text on physical geography or geology
to help in understanding the terms and concepts here.
1. Landforms
Contour lines and other map symbols can give you clues about
the geology and geomorphology that underlies the landscape. In
general, rocks differ in their resistance to weathering and
erosion, and these differences are reflected in the landscape.
Some examples:
Fault lines. Some faults can sometimes be seen on a map
where streams have been offset to the left or right along a line,
then continue downstream. These are strike-slip, or transform,
faults, where one section of the crust is sliding past another.
California's San Andreas and associated faults are examples of
transform faults. In other faults, one section of the crust slides
under another. These normal or reverse faults are usually less
visible unless considerable uplift has occurred. Death Valley is
the result of a pair of normal faults letting the valley floor
downward several thousand meters.
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Cuestas and hogbacks. These are the result of a
block of terrain being tilted upward at one end. The
result is a gradual upward slope with a cliff at the
uplifted end. Good examples of these can be found in the
desert Southwest.
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Volcanoes. In contrast to most hills, volcanoes are
usually much rounder, so that contour lines around them are
circular.This is especially true for stratovolcanoes, the most
violent and prominent volcanoes.
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Examples are Mt. Shasta in California and Mt. Rainier
in Washington. Some volcanic eruptions are gentler and
form gentler hills or even broad plateaus. These flows
are more difficult to detect from the topographic map,
unless the USGS adds a dotted pattern that indicates a
lava flow.
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Wave action. Waves are very efficient at cutting back into
cliffs. The waves crash against the base of the cliff and undercut
the cliff. Eventually a chunk of cliff topples into the sea.
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But waves don't cut down much below sea level,
especially where the rock along the shore is relatively
hard. The result is that wave action can create a long
wave-cut platform or terrace along the shore. These
platforms are often visible on coastal maps.
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If the coast is uplifted, this flat wave-cut (or marine) terrace
can be high and dry above the ocean. The California coast has been
rising relative to the sea over the past several hundred thousand
years. In many areas a series of terraces are visible on maps and
in person. The Sea Ranch, along the coast in northern Sonoma
County, is built on a marine terrace.
Glaciation. Glaciers can occupy either mountainous or
flat terrain, and result in corresponding alpine or continental
glacial features. Many kinds of features can result, so I'll
mention only a couple of examples. For alpine glaciation, the ice
will occupy a valley and hollow out its sides and head. This turns
the valley from V-shaped to U-shaped, with steep sides and flat
bottom.
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Small lakes may form in the valley, known as tarns. As
it excavates into the mountain at the head of the valley,
another glacier may be doing the same on the other side
of the mountain. This results in a sharp ridge, or arete.
If three glaciers surround and erode a mountain, they may
form a three-sided peak, known as a horn (the Matterhorn
is the best-known example). California's Sierra Nevada
was covered by glaciers during the last glacial peak
(about 15,000 years ago), and many of these features
remain as evidence.
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Continental glaciers, or ice sheets, produce different landforms.
The most striking is where the glacier's front has remained
stationary for a long period. The glacial ice will be moving
forward toward the front, carrying rock and debris in the ice. The
ice melts at the front and leaves the debris as a moraine.
Moraines are hilly ridges perhaps a mile wide and up to several
hundred miles long. They may have a hundred feet of local relief
(vertical elevation change). The ridges contain many depressions
that fill with water. If you see a map with irregular hills and
many small lakes, glaciation may be the cause. Ice sheets covered
most of the upper Midwest, down to about the Missouri and Ohio
Rivers. Nearly all of Minnesota's 10,000 lakes were formed by
glaciers. California didn't have any continental glaciation to
speak of--only alpine.
Karst. Another type of area with irregular terrain,
sometimes with many lakes, is known as karst. Karst forms in
limestone and other rock that easily dissolves in water. The water
dissolves both the surface and the subsurface. Caves result below
the surface--most caves are formed in limestone rock (Carlsbad
Caverns, Mammoth Cave, etc.).
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But the surface may also show the result of being
dissolved: sinkholes (small depressions) and disappearing
streams (where a stream suddenly vanishes) are evidence.
Karst is common in Indiana, Kentucky, Arkansas, Missouri,
and Florida (where houses have been swallowed by
sinkholes). California has a small area of karst in the
Marble Mountains, in the extreme northern part of the
state.
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Winds. Winds rarely shape the landscape enough to show on
topographic maps. The exception is in areas with accumulations of
loose sand, which wind can move effectively. Sand may accumulate
in deserts, along shores, or where the bedrock is sandstone. The
wind usually shapes the sand into dunes. There are many types of
dunes, mostly due to different wind speeds and directions. Often
the wind is consistent enough from one direction to line up the
dunes, so a linear pattern shows up on the topographic map.
Streams are usually absent or rare, since water flows into and
through the dunes easily. Topographic maps usually show sand dunes
with a distinctive dotted pattern. Large sand seas are found in
the Nebraska Sand Hills, White Sands National Monument, and
southeastern California.
Mass movement. Gravity affects all events on Earth, but
it is the defining force in mass movement. Landslides, rockfalls,
and slumps are all examples of mass movement. When a slope becomes
too steep for the cohesive forces retaining it, it gives way. The
reasons for gravity overcoming the slope can include uplift from a
fault, an earthquake, a stream undercutting a slope, burning of
vegetation that holds the slope, or excavation by humans. Small
mass movements may be too small and temporary to be visible on a
topographic map. Large landslides and slumps may be evident,
especially in certain areas where they are frequent. Mountains are
good candidates. Sonoma County is also prime terrain, as winter
rains saturate hills that have been overgrazed, undercut or built
upon.
2. Drainage Patterns
The terminology of drainage patterns is not particularly useful
in and of itself. But drainage patterns can suggest what is
happening with the underlying geology and landscape.
Dendritic. The "normal" pattern of stream drainage is
called dendritic, since it looks like a tree's roots or branches.
This pattern occurs when no strong geological factor controls the
drainage network.
Meandering. A stream that has had a chance to erode for
a long period tends to widen its path across a large floodplain,
and meander back and forth across the floodplain. These streams
usually flood periodically and fill their floodplain. While unwise
to build on the floodplain, the land is usually flat and fertile,
and tempting for short-sighted settlers. These streams are often
channelized into straight courses. This rids the local area of
water quickly but creates even more flooding downstream.
Braided. Some streams in floodplains have many small
channels that merge and separate downstream. Braided streams are
most common where the water flow is variable (e.g., deserts or
mountains) and the stream bed is mostly sand and gravel.
Trellis & Rectangular. These patterns are where
streams flow in straight segments and turn at sharp angles.
Usually this results from sedimentary bedrock controlling the
direction of streams along the surface. Good examples of trellis
drainage are found in eastern Pennsylvania, where folded
sedimentary rocks cause streams to flow at right angles to each
other.
Radial. Radial drainage occurs around circular hills and
mountains, with streams radiating out in all directions. This
would be typical around a volcano.
Centripetal. The opposite of radial, here streams drain
inward toward a central basin. The basin usually has a dry or
saline lake and has no outlet--a sign of arid conditions.
Deranged. Streams have no organized pattern. Some drain
externally toward major rivers, others may drain internally. This
is usually a sign of continental glaciation, or possibly sand
dunes or karst.
Artificial. Human-caused modifications of streams
include channelized streams (straighter than any normal stream),
canals, drainage ditches (may be a sign of natural wetlands),
reservoirs (which not only have a dam, but usually a more indented
shoreline than a natural lake), and levees.
3. Vegetation
USGS topo maps often contain some indication of vegetative
cover, but not always. Older maps lack this information, and some
kinds of vegetation aren't indicated.
Forest and woodland. USGS maps indicate forest or
woodland (area with trees but not continuous canopy cover) by a
uniform green tint. The size, orientation and shape of tree cover
can tell us about climate and land use. Types of cover patterns
include:
- Treeline forests, in higher elevations where cold climate
prevents trees from growing any higher;
- Moisture-favorable forests, in canyons, ravines, on slopes
away from the Sun (especially north slopes), or up slopes in
arid lands;
- Dry-land forests, on drier islands in wetlands; good
examples may be seen in Florida's Everglades, in "mahogany
hammocks";
- Landslides or avalanche chutes, where falling rock or snow
keeps areas clear of mature trees;
- Human-caused forest patterns, including clearcuts with
sharp edges in otherwise forested land; bottomland forests in
wet areas where the surrounding land has been cleared; and
woodlots, shelterbelts and windbreaks around farms and
ranches.
Orchards and vineyards. USGS topos give these
distinctive patterns of regular dots. It is interesting to examine
where these have been placed on the terrain--usually up above the
valley floor slightly to avoid cold-air drainage that occurs at
night.
Scrub. Scrub or shrub vegetation has an
irregularly-dotted pattern. Chaparral vegetation in California
normally has this pattern, although it is not always mapped.
Chaparral is a sign of Mediterranean climate, that is, mild, wet
winters and warm, dry summers. Soil is also a factor. For example,
in our area, soils that dry out thoroughly in summer are more
likely to harbor chaparral.
Wetland vegetation. USGS topographic maps have
distinctive symbols for wooded wetland (also called swamp),
nonforested marsh, and mangroves. Mangroves are shrub or small
tree-sized plants that grow directly in warm salt water along
tropical and subtropical coasts. Florida and other Gulf Coast
states have many mangrove areas, although many have been cleared
for development.
B. Cultural Features
1. Transportation Patterns
Besides the types of roads listed in the key for topographic
maps (primary, secondary, light-duty, unimproved), look also at
the placement of the road. It may follow along elevation contours,
even if the route is circuitous--an indication of steep terrain,
relative to the amount of traffic carried. Heavily-traveled routes
tend to get straightened.
Other areas may have roads that follow flat terrain, and cross
steep slopes only when connecting level areas. The flat areas are
either valley floors, with few roads going over mountains, or
mesas or interfluves, where the flat land is dissected by streams.
The Appalachians are good places to find transportation along
valleys. A glance at a road map of eastern Pennsylvania will
indicate that valleys and hills trend from southwest to northeast.
Southern California has good examples of mesas, most of which are
marine terraces formed long ago and since lifted above the
sea.
Grid patterns are the rule where areas were surveyed before
settlement, as in most lands under the Public Land Survey system.
Roads in these areas often follow the square grid regardless of
terrain.
Don't overlook other kinds of transportation, such as
railroads, canals, and trails. These often indicate something
about the history or land use of an area. A map with many
railroads, for example, likely says the area was important during
the early 20th Century. You also may notice corridors that used to
be railroads--often shown as "old railroad grade." Many of these
are being converted to foot trails or bicycle paths. Canals for
transportation are rarely built nowadays, but were popular in the
19th Century.
2. Rural Settlement
Rural housing. Rural houses and buildings are usually
shown on topographic maps as small black squares. Rural settlement
patterns usually reflect the original land survey. Regions
surveyed under the PLS started out with a very dispersed
settlement pattern. Homes were scattered on farms and ranches,
usually no more that four per square mile. Areas surveyed under
irregular survey systems (metes-and-bounds, land grants, etc.)
tend to have homes more clustered, or along roads that went
through or around land parcels. Land in long-lot surveys typically
has houses closely spaced along a few main roads or rivers, with
few houses elsewhere.
Service facilities. Along major transportation routes in
rural areas, small settlements sprung up to service travelers and
their vehicles. These settlements concentrated at railroad
stations in the 19th and early 20th Centuries. As the automobile
became the primary means of transporting people in the mid-20th
Century, service facilities became more dispersed along highways.
With travel more concentrated on interstate highways, facilities
and settlements are once again becoming more concentrated, this
time at major exits on interstates.
Urban invasion. Many rural areas have been "invaded" by
urbanites for summer or weekend homes, or even long-distance
commute homes. Lakes and rivers are popular places, especially in
more arid regions of the West. Campgrounds, resorts, and other
tourist facilities have expanded rapidly in the past few decades.
A dense pattern of these indicate either a nearby metropolitan
area (such as Sierra Nevada resort areas), an unusually popular
location (such as Yosemite or Redwood parks), or a wealthy
clientele (such as Aspen or Vail).
3. Urban Development
The patterns of streets and facilities in urban areas can
suggest much about the function and history of the city. Often you
must investigate the particular groups that settled the area to
fully appreciate the patterns. The myriad groups who immigrated to
the US brought their own traditions of land-use. Of particular
influence were the English, French, German, and Spanish. Subtle
influences of others, such as Native Americans or Asians, can
sometimes be detected.
Irregular street patterns. Early in our history, streets
were laid out according to the major trading routes and the shape
of the land. This produced an irregular pattern, especially in
smaller towns.
Regular grid patterns. Most cities adopted regular
grids for streets to make surveying and development easier. This
is particularly true in PLS areas. At first, street grids were
oriented with respect to the major transportation line, even if
the line went northwest-southeast. Later, most street grids were
oriented north-south and east-west. The changing pattern can be
seen in many cities as they grew outward from the center.
Irregular patterns, again. In the past few decades, the
regular grid of street became associated with uniform houses and
middle-class lifestyles. Wealthy people (and some who want to look
like they are) like to distinguish themselves from ordinary folk,
and have used winding, irregular streets for their housing to do
so. This also goes along with the trend in the US for wealthy
people to live in hills above the city; regular grids would be
difficult here anyway.
Industrial areas are often visible on topographic maps
as clusters of larger buildings, and may help discern the area's
function. Economic geographers often divide industries into raw
materials-oriented, such as gravel pits and food processing
plants; those in manufacturing, which often cluster together where
power, labor or transportation is available; and market- and
service-oriented, which cluster where customers are, for example
bottling plant, shopping malls and strip developments.
4. Place-names
Place-names often give clues about the area's history or
occupants. Often this can suggest a series of different groups in
an area, or sequent occupance in geographic jargon. In California,
of course, many names reveal the Spanish and Mexican
presence--which is both historical and continues today. Town names
are not the only clue. Other words were applied to places and have
stuck, sometimes as more reliable than city names. For example, I
doubt many of these communities were founded by Spanish-speakers:
Del Mar, Tierrasanta, San Anselmo, El Cerrito, San Carlos and
Rancho Mirage. On the other hand, words like verde, agua, mesa,
arroyo, iglesia, and oso occur on maps as part of other names and
indicate early settlement by the Spanish. Laguna lake is
redundant--laguna means lake in Spanish--and the name may reveal
an early Spanish presence.
Other groups settled throughout the US, and even California.
Groups including French, German, Czech, Swedish, Norwegian,
Danish, Irish, Polish, Chinese, Korean, Japanese, and recently
Vietnamese and Hmong have established place-names. The Russians
colonized the northwestern coast of North America in the early
19th Century, and some place-names remain even where few Russians
do (Sitka, Petersburg, Soldotna, Andreanov Islands, etc.).
Sebastopol, however, is a later revision having nothing to do with
the Russian city other than the name itself.
5. Mining
Mining operations disturb local areas, sometimes severely.
Topographic maps often show mining pits with a distinctive shading
pattern (see Topographic Map Symbols brochure). Gravel pits and
quarries also receive a point symbol. We could also include oil
and gas wells here, indicated on topo maps; presence of many such
wells suggest a major contribution to the local economy.
Oftentimes other clues also reveal mining, especially past mining:
irregular contours that do not match the general trend of the
landscape, unexpected depressions shown by contours, and rail
lines or roads dead-ending in the area. Large mines, such as strip
mines in the Appalachians and open-pit copper mines in Arizona
show these features prominently on topo maps.
Topographic maps can be a rich source of information
about a landscape, even absent other information. It is a good
idea to use collateral information, such as histories or
geographies of an area, before sharing your conclusions with
friends and relatives. Remember, maps are representations of
reality, not reality itself!
Appendix
Table of Equivalents
1000 micrometers = 1 millimeters (mm) 6 miles = width of
township
0.3937 in = 1 centimeter (cm) (10 mm) 36 sections = 1
township
2.54 cm = 1 inch 1 section = 1 mi2 (usually)
39.37 in = 1 meter (100 cm) 43,560 ft2 = 1 mi2
63,360 in = 5,280 feet = 1 mile 6373 km = 3960 mi = mean polar
radius
0.6214 mile = 1 kilometer (1000 m) of Earth
1.609 km = 1 mile 6,356.6 km = Earth radius at Pole
6.45 cm2 = 1 inch2 (Clarke Ellipsoid)
0.155 in2 = 1 cm2 6,378.2 = Earth radius at Equator
0.092 m2 = 1 foot2 (Clarke Ellipsoid)
10.764 ft2 = 1 m2
2.471 acres = 1 hectare
10,000 m2 = 1 hectare
2.59 km2 = 1 mile2
640 acres = 1 mile2
Bibliography
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