MODULE 1 -
INTRODUCTION
TO SITE
SURVEYING
cont…
Scales
WHAT IS A SCALE?
• A proportional representation on paper/drawing of the
actual dimensions of a horizontal distance measurement of
a physical structure or element.
• The ratio of the dimension on a map or plan to the same
dimension on the ground is thus called a scale.
• A scale is the size that is used in the drawing that is smaller
than the actual size of a structure but represents the actual
size of the structure on the ground. The size used must
match the real size of the structure.
• A building is much bigger than it can be shown on a construction
drawing.
• But the correct measurements, sizes, heights and shapes of the real
building must be shown on the drawing so that these can be used to
carry out construction activities correctly.
• Architects and engineers use a scale on the drawing which helps
them to reduce everything in the correct proportion to how the
structure will be on the ground.
• The drawing is drawn to scale. In other words, it uses the correct
measured proportion.
• The scale used is shown as a ratio, e.g., 1:100. This means that 1
measured unit on the drawing/plan is equal to (:) 100 measured on the
land/ ground.
• For a project that is on a large site the architect or engineer will use a
smaller scale such as 1:500 so that everything can be shown on one
drawing.
• For a project that is on a smaller site, the architect or engineer will use
a larger scale, such as 1:10.
• The scale used should be shown on the title page or on the title block
at the bottom of the drawing.
• There should be a note saying what unit of measurement the architect
is using in the scale, e.g. millimetres (mm) or metres (m).
• A scale is described as one in one hundred but is written as 1:100. e.g. a
scale of 1:100 means that 1 unit on the drawing, map or plan represents
100 units on the ground.
Examples:
• 1m on plan = 200m on ground
• 1mm on plan = 200mm on ground
These are called natural scales.
• Engineering scales are the relation between two different units in
measurement, one referring to the map, the other to the ground
measurement.
A. Engineer’s scale : 1 cm = 50 m
B. Representative Fraction (R.F) :
It is the ratio of the distance on the map to the corresponding distance
on the ground taken as same units. Scale of 1 cm = 50 m, 1 cm on the
map represents 50 m (5000 cm) on the ground. Therefore, the
representative fraction (R.F.) is 1/5000 or 1: 5000.
WHY DRAWINGS ARE DRAWN TO SCALE
• It is very important that all construction drawings are drawn to
scale and that they correctly show or represent the real
measurements of structures on the ground.
• The entire construction team will use the scale to:
• Understand the size of the project and the type of work to be done.
• Measure the length of something on the drawing and then convert this
measurement to actual length on the site.
THE IMPORTANCE OF AN ACCURATE SCALE
• An architect uses a special ruler called an architect’s scale to accurately measure
and use the reduced scale on drawings.
• This scale is calibrated (to set or adjust a measuring instrument so that it gives an
accurate reading) or has a set of markings in millimetres and metres on it, that are
used to make accurate measurements.
• An architect’s scale can have different shapes so that different scales can fit onto it,
e.g., it can be flat or triangular. A flat scale may show pairs of ratios on it, i.e. :
1:1/ 1:100
1:5/ 1:50
1:10/ 1:100
1:20/ 1:200
1:250/ 1:2 500.
• Triangular scales also show pairs of ratios, i.e.:
1:1/ 1:10
1:2/ 1:20
1:5/ 1:50
1:100/ 1:200
1:500/ 1:1 000
1:1 250/ 1:2 500
• Architects need to know which scale they are using on the ruler and on
the drawing, and they also need to note on the plans whether the scale
is in millimetres or metres.
• Millimetres are usually used on scales between 1:1 and 1:100.
• In other words, every 1 measured unit on the drawing/ plan equals 100
millimetres or lower depending on the scale.
• Remember that there are 1 000 millimetres in a metre.
• Usually, the metre is used for scales over 1:200.
• So, every 1 measured unit on the drawing/plan equals 200 metres.
COMMONLY USED SCALES
• Different scales are used for different drawings in a set.
• The following table shows the recommended or most common scales
used in architect drawings for different types of plans.
Site plans Layout drawings Plumbing and drainage
installation
1:100; 1:200; 1:500; 1:20; 1:50; 1:100 1:50; 1:100; 1:200
1;1 1000
• A drawing that does not use any scale is labelled Not to Scale or NTS.
SCALES APPLICABLE TO TYPE OF DRAWING
TYPE OF DRAWING SCALE
Working drawings
Locality plan 1: 1 000 or smaller
1: 100
Site plan 1: 500
1: 200
1: 1 000
Layout drawings: (plans; sections; and 1: 20
elevations)
1: 100
1: 50
Component drawings: (ranges; details; 1: 50
assembly)
1: 20
1: 10
1: 5
1: 2
1: 1
THE DISTINCTION BETWEEN MAPS AND PLANS
• A map is a representation of an object, no matter how accurately
it may be shown. As an example, a winding country road about
the width of a car measures almost a metre on a 1:50 000 map.
This represents 50 metres on the ground, far in excess of the
actual width of a road.
• A plan accurately defines widths of roads, sizes of buildings etc;
in other words, every feature is true to scale. Site plans are large
scale productions and are essential to the planning and
development of a construction project.
THE DISTINCTION BETWEEN MAPS AND PLANS
1. A map is a visual representation of an area—a symbolic
depiction highlighting relationships between elements of that
space such as objects, regions, and themes.
Plans are a set of two-dimensional diagrams or drawings used to
describe a place or an object, or to communicate building or
fabrication instructions. Usually, plans are drawn or printed on
paper, but they can take the form of a digital file.
Map
Building Plan
2. Although most commonly used to depict/ to show geography, maps
may represent any space, real or imagined, without regard to context or
scale.
Plans are often for technical purposes such as architecture, engineering, or
planning. Their purpose in these disciplines is to accurately and
unambiguously capture all the geometric features of a site, building,
product or component.
Plans can also be for presentation or orientation purposes, and as such are
often less detailed versions of the former. The end goal of plans is either to
portray an existing place or object, or to convey enough information to
allow a builder or manufacturer to realize a design.
3. Many but not all maps are drawn to a scale, allowing the reader to infer or
to assume the actual sizes of, and distances between, depicted objects.
A larger scale shows more detail, thus requiring a larger map to show the
same area.
Plans are usually to scale drawings, meaning that the plans are drawn at
a specific ratio relative to the actual size of the place or object.
Various scales may be used for different drawings in a set. For example, a
floor plan may be drawn at 1:50 whereas a detailed view may be drawn at
1:25. Site plans are often drawn at 1:200 or 1:100
4. To communicate spatial information effectively, features such as
rivers, lakes, and cities need to be labeled. Over centuries cartographers/
mapmakers have developed the art of placing names on even the densest
of maps.
Because plans represent three-dimensional objects on a two-dimensional
plane, the use of views or projections is crucial to the legibility of plans.
5. A plan is a true scale representation while a map is drawn such that
some features on it cannot be drawn to scale.
On a map many features are represented as symbols and generalization
is carried out resulting in changes in scale and displacement of features.
e.g on a 1:1 million map, rivers and roads may be shown but they
cannot be drawn to scale. a 5m road would be 0.005mm wide if drawn
according to scale.
IMPORTANT NOTES
• When more than one scale is used on a drawing, state the general scale in
the title panel and clearly indicate the other scales in prominent positions
adjacent to the appropriate details.
• For sections of drains, sewers, earthworks, etc. where horizontal and
vertical scales are used, it is convenient to use an exaggerated vertical
scale to show clearly differences in levels at each distance (chainage
point).
• When parts of a drawing are not drawn to scale, add NTS (i.e. not to
scale) after the dimension numerals.
CALCULATION OF SCALES
𝑺𝑪 = scale as representative fraction
1
e.g. 1: 200 would be written as
200
NOTE:
• 1m on the plan equals 200m on the ground
• 1mm on the plan equals 200mm on the ground
𝑴𝑷 = Measurement on plan
𝑴𝑮 = Measurement on the ground
FORMULAE
𝑴𝑷
𝑺𝑪 =
𝑴𝑮
NOTE: 𝑴𝑷 & 𝑴𝑮 must be in the same units
EXAMPLE 1:
A building is 50m in length. What is its length on a plan of a scale 1:100?
𝑪 𝑴𝑷
𝑺 = 𝑮
𝑴
𝟏
Given: 𝑺𝑪 =
𝟏𝟎𝟎
𝑴𝑮 = 50m
𝟏 𝑴𝑷
=
𝟏𝟎𝟎 𝟓𝟎
𝟓𝟎
𝑴𝑷 = (Changed subject of the formulae or
𝟏𝟎𝟎
balanced equation)
𝑴𝑷 = 0.5m
Thus the length of the building on the plan is 0,5m or 0,5m x 1000 = 500mm
EXAMPLE 2:
A line X to Y on a plan of scale of 1:200 is 400mm. Find the length on the ground in metres.
𝑺𝑪 = 1: 200
𝟏
𝑺𝑪 =
𝟐𝟎𝟎
𝑴𝑷 = 400mm
= 0,4m (Changed MP into metres divided by 1 000)
𝑪 𝑴𝑷
𝑺 = 𝑮
𝑴
𝟏 𝟎,𝟒
=
𝟐𝟎𝟎 𝑴𝑮
𝑴𝑮 = 0,4 x 200
𝑴𝑮 = 80m
EXAMPLE 3:
A line on the plan is 15cm and on the ground is 300m. Find the scale that should be on the
plan.
Given: 𝑴𝑮 = 300m
𝑴𝑷 = 15cm
𝑴𝑷 = 0.150m (NB: All the same units)
𝑪 𝑴𝑷
𝑺 = 𝑮
𝑴
𝟎.𝟏𝟓𝟎
𝑺𝑪 =
𝟑𝟎𝟎
𝟏
𝑺𝑪 =
𝟐𝟎𝟎𝟎
or
𝑺𝑪 = 1: 2000
SELF EVALUATION EXERCISES
1. A line measures 15cm on a plan drawn to a scale of 1/2500. What is the length of the line on
the ground.
2. A plan is drawn to a scale of 1:400. Determine what 1cm or 10mm represents on the ground.
3. A line of 100mm is drawn on a plan of scale 1: 200. Determine the actual length the line
represents.
4. A square plot of land has an area of 16m2. If the land has to be represented on a plan with a
scale of 1: 150, find the length of a side on a plan in mm.
5. A circle has a circumference of 62.832m. This is to be represented on a plan of scale 1: 250.
Find the length of the diameter on plan in mm and cm.
6. The following triangle was drawn on a plan of scale 1: 2000. What is the length of its side
and its p/d height?
ANSWERS
1. 375m
2. 4m
3. 20m
4. 26,7mm
5. 80mm and 8m
6. 260m ; 225m (225.167m)
THANK YOU!!!!
