Lect-10 (Geological Maps)

MAP
A map is a symbollic represenntation of seelected charracteristics of a place, usually draawn on a

flat surfface. Maps present infformation aabout the earth in a siimple, visuaal way. They teach
about thhe earth by showing sizes and shaapes of coun ntries, locattions of feattures, and distances
d
betweenn places.
Some coommon feattures of map

ps include sscale, symbols, and grids.
Scale
All mapps are scale models of reality.

r Am map’s scale indicates
i thee relationshhip between the
distancees on the maap and the actual
a distannces on Earrth. This relaationship caan be expresssed by
a graphiic scale or a representaative fractionn.
The moost common type of graaphic scale llooks like a ruler. Also
o called a baar scale, it is simply
a horizoontal line marked
m off in meters, kkilometers, or
o some othher unit of mmeasuring distance.
d
The reppresentative fraction do oes not havee specific un nits. It is shown as a frraction or raatio—for
examplee, 1/1,000,0000 or 1:1,0 000,000. Thhis means th hat any giveen unit of mmeasure on the map
is equall to one milllion of that unit on Earrth. So, 1 ceentimeter on n the map reepresents 1,,000,000
centimeeters on Eartth, or 10 killometers.
The sizee of the area covered helps

h determ
mine the scaale of a map
p. A map thhat shows ann area in
great deetail, such as a street map of a neighborho ood, is called a large--scale map because
objects on the mapp are relativvely large. A map of a larger area, such ass a continen nt or the
world, is called a small-scaale map bbecause objjects on th he map are re relatively
y small.
1
Symbols
A map usually has a legend, or key, that gives the scale of the map and explains what the
various symbols represent.
Some maps show relief or changes in elevation. A common way to show relief is contour
lines, also called topographic lines. These are lines that connect points that have equal
elevation. If a map shows a large enough area, contour lines form circles.
A group of contour line circles inside one another indicates a change in elevation. As
elevation increases, these contour line circles indicate a hill. As elevation decreases, contour
line circles indicate a depression in the earth, such as a basin.
Grids
Many maps include a grid pattern, or a series of crossing lines that create squares or
rectangles. The grid helps people locate places on the map. On small-scale maps, the grid is
often made up of latitude and longitude lines. Latitude lines run east-west around the globe,
parallel to the Equator, an imaginary line that circles the middle of the Earth. Longitude lines
run north-south, from pole to pole. Latitude and longitude lines are numbered. The
intersection of latitude and longitude lines, called coordinates; identify the exact location of a
place.
Map Projection
Map projections try to portray the surface of the earth or a portion of the earth on a flat piece
of paper or computer screen. A coordinate reference system (CRS) then defines, with the help
of coordinates, how the two-dimensional, projected map in your GIS is related to real places
on the earth. The decision as to which map projection and coordinate reference system to use,
depends on the regional extent of the area you want to work in, on the analysis you want to do
and often on the availability of data.
The process of creating map projections can be visualized by positioning a light source inside
a transparent globe on which opaque earth features are placed. Then project the feature
outlines onto a two-dimensional flat piece of paper. Different ways of projecting can be
produced by surrounding the globe in a cylindrical fashion, as a cone, or even as a flat
surface.
2
The thrree familiess of map pro
ojections. T
They can be represented d by a) cylinndrical projeections,
b) con
nical projecttions or c) planar
p projections.
EXAMPLES
1. A disstance is meeasured 125
50 m on the field and sh
hown 5 cm on the mapp. What is th
he scale
of the m
map?
5 cm 1250000 cm
1cm X cm
m
X= 25000 cm scalee: 1/ 25.000
2. A meeasured distance of 8 cm
m on 1/25.0000 scaled map
m is how many km oon the field??
1 cm
m 250000cm
8 cm
m X
= 200000 cm = 2 km
X=
3. A meeasured disttance of 500

00 m on thee field is how
w many cm
m on 1/25.0000 scaled map?
1 cm
m 250000 cm
X cm
m 50000 cm
m
X= 20 cm

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MAP

A map is a symbollic represenntation of seelected charracteristics of a place, usually draawn on a

Some coommon feattures of map

All mapps are scale models of reality.

The sizee of the area covered helps

X= 25000 cm scalee: 1/ 25.000

3. A meeasured disttance of 500

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