MAPS, PLANS AND SCALES
Definition of Maps
Purposes of Maps
Types of Maps
Difference between map and
plan
Depiction of surface relief
Conventional signs
Definition of scale
Types of scale
Exercise
Definitions
2
A map may be defined as representation to scale of
features of the surface of the earth.
Maps at very large scale e.g. 1:500, 1:250 are
referred to as plans and show details precisely with
no exaggeration and little variation from ground
shapes.
Cartography is the making and study of maps in all
their aspects.
Maps and Plans
3
Concerned with locations and attributes at locations
Locations being positions on a 2D space with
coordinates
Attributes at locations being qualities or magnitude
from which relationships can be found e.g. distances,
directions, heights, etc.
Maps and Plans
4
Map and plans are reductions
Have defined dimensional relationship between map
and reality - scale
Scale limits information put on map. Data is
classified, simplified and symbolised.
Involve transformation i.e. from spherical to plane
map projection.
Map projection affect use. Maps have Spatial
Reference Systems or Coordinate Systems which
assist map users to determine positions, elevation,
direction, size etc.
Map Projection
5
Map projection is the orderly
transfer of positions of places on
the surface of the earth to
corresponding points on a flat
sheet of paper, a map.
Projections bring some degree of
distortion in a map in terms of length,
angle, shape and area.
Most common projections used in
surveying are Tranverse Mercator
and Lambert Conical Projections.
Purposes of a Map
6
To store geographic information in
spatial format.
To serve mobility and navigation
needs.
To summarise statistical data and,
thereby, assist in spatial forecasting
and spotting trends.
Provides information in a simplified
way.
Types of maps
7
General Reference Map
Maps which show location of a variety of different
features, such as water bodies, coastlines, and
roads, e.g. maps of states, countries or continents.
Large scale general reference maps are called
topographic maps.
General reference Map – North
8
America
General Reference Map- World
9
Types of maps
10
Topographic
maps depict as
much of the
surface features
of a particular
area as is
possible within
limitation of
scale e.g. village
map.
Types of maps
11
Thematic or Special purpose maps
These are maps that
concentrates on the distribution
of single attribute or
relationship among several.
The common factor about such is
that they have single theme of
study e.g. maps of temperature,
population, land utilisation.
Thematic Map - Population density
12
by State
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Sea and Air Charts
14
Designed to serve the needs of navigators i.e.
nautical and aeronautical.
One distinction is that maps are looked at, while
charts are to be worked on.
On charts, navigators plot their courses, determine
positions, mark bearing, etc
Sea Chart
15
Types of maps
16
Difference between Map and Plan
17
On maps the scale is too small to allow every
feature to be properly represented to scale, thus
symbols are used to represent too small features to
be recognised.
Plans show all features on the ground correctly to
scale.
Maps are normally at small scale, where as plans
are drawn to a much larger scale.
Cadastral Plan
18
Difference between Map and Plan
19
Due to limitations of scale, maps tend to generalise
and exaggerate features while plans show features
in their true shape and position.
Plans, do not only show existing terrain condition but
also depict proposed alterations to the existing
landscape.
Depiction of Surface Relief
20
On large scale and small scale maps there are 3
methods of showing surface relief.
Contour lines
A contour line is a line joining points of equal height
above mean sea level.
Spot levels
As the name would imply, a spot level is imply a dot or
spot on the map, the level of which is printed alongside,
and is used to show variation of elevation on large-scale
maps.
Depiction of Surface Relief
21
Bench marks
Bench marks are permanent marks on
the ground sometimes chiseled on
buildings showing the height of that
particular point above Surveys and
Mapping Datum.
Surveys and Mapping datum is the
point of reference to which all bench
marks , spot levels, and contour lines
are referred, and is the mean sea
level of the sea as recorded over
many years at Cape Town.
Conventional Signs
22
Since it is impossible to truly to represent each
individual feature on any map, a code of signs has
been devised for use with each scale of DSM maps.
As far as possible, the signs are a representation of
the actual object.
To simplify printing initials of the features are used
e.g. T for telephone booth.
Scale
23
Scale is defined as the relationship between distance
measured on the map and true distance on ground.
Representation of Scale
Expressed in words
e.g.1mm represent 500m
Drawn by scale bar
Representative fraction
or ratio
e.g 1/5000 or 1:5000
Classification of maps by scale
24
In connection with map scale the words ‘small’,
‘medium’, and ‘large’ are frequently used. There is
little agreement as to where the dividing line come.
The table below can used as a guideline
Classification of maps by scale
25
Category Scale
large scale 1:100, 1:500
1:1000
Medium scale 1:5000, 1:10000
Small scale 1:25 000
1:50 000
1:250 000 or more
Exercise
26
a) A distance between points A and B is measured
to be 10cm. What will be the equivalent
ground distance if map scale is 1:500, 1:1250?
Your answer should be in metres.
b) An area was measured on the plan by a rule as
250x175mm. Calculate the ground area in
square metres I the scale is 1:2000; 1:500.
Exercise
27
c) The scale of a plan is 1:200. The distance
between the two points X and Y on the plan
measures 435mm. Calculate the actual ground
distance.
d) In a town centre redevelopment, an existing war
memorial is to be replaced by a new concrete
one. A model of the concrete block scale 1:5 has
the dimensions 1 metre high by 500mm wide by
500mm long. If the concrete model weighs 500kg
calculate the dimensions and weight of the real
memorial.
Exercise
28
e) An area of ground lying between a straight
road and a boundary fence has an actual area
of 6250 square metres.
i) The area, as measured on an old plan
whose scale has been obliterated, scales
1000 mm². What is the scale of the old plan?
ii) The main survey line runs along the edge of the
road. If the distances from the ends of the survey
line to the boundary are 36.90 and 25.60m
respectively, measured at right
Exercise
29
angles to the survey line, calculate the length of the
main line.
f) The dimensions of a room on a 1:50 plan are 60
mm x 85 mm. Calculate the area of the room in m²?
