Civil Engineering Department
TOPIC-MAP READING
SEMESTER-4TH
BY
Mrs. MANDAKINI MOHANTA
(LAB ASST. civil eNgineering department)
AY:2021-2022
WHAT IS A MAP?
HISTORY:
FINDING YOUR POSITION ON EARTH
Longitude lines – also called Meridians, are circular. These run North to South. The Prime Meridian runs through Greenwich, UK & is numbered 0.
Latitude Lines – these are parallel to the Equator which runs around the Earth at 0 degrees. This splits the Earth into two parts, these being the Northern & Southern Hemisphere.
RECORDING A POSITION
If you put the latitude & longitude lines together on the same globe you will get a Matrix. With this system you can give a point’s exact position by stating its latitude, followed by its longitude in degrees & minutes.
MAPS
Today, every area of ground is covered by either survey or by satellite to give up to date maps of the world.
Ordnance Survey – The UK is fortunate because it is served by possibly the best cartographers anywhere. The Ordnance Survey (OS) is a Government department based in Southampton. They produced their first map in 1791 for the Army.
The maps that are mostly used within the ATC are Metric 726 series – 1: 50,000.
WHAT YOU WANT FROM A MAP
If you need to get from A to B it is important that you find the best route so that you can avoid rivers, motorways and other such obstacles.
By the end of this lesson you should be able to read a map, that will include:
Symbols Grid References Distances
The M726 Series Map is classed as a Topographical map which means it shows the shape & surface detail of the land, including natural & man-made features.
A typical map would show:
Rivers Valleys Hills Streams
Woods Mountains Marshes
Man-made features would include:
Roads Canals Railways Towns
Villages Power lines
TYPES OF MAP
The M726 Series is not the only type of Map available, there are maps for several other user groups:
MAP SELECTION
The map you use will depend on the activity undertaken:
SCALE | POSSIBLE USE | |
1: 10 000 | 1cm = 100m | Orienteering, town planning |
1: 25 000 | 1cm = 250m | Walking |
1: 50 000 | 1cm = 500m | Walking |
1: 63 360 | 1 inch = 1 mile | Walking |
1: 100 000 | 1cm = 1000m | Cycling, route planning |
1: 250 000 | 1cm = 2500m | Cycling, motoring, flying |
1: 1 000 000 | 1cm = 10km | Long distance Air Navigation |
MAP LANGUAGE�Map Layout & Features
KEY:
MAIN ELEMENTS OF A MAP
Elevation
When using a map you firstly check the units of height or elevation. This will be displayed in either feet or metres.
Latitude & Longitude
Latitude is expressed in degrees & minutes and marked along the right & left (East & West) hand side of the map. Longitude lines are marked along the top & bottom (North & South) of the map. These lines are not drawn on the map itself – it would be too confusing.
North References:
True North – Geographical North pole of the Earth – the point where the Earth’s axis meet the surface.
Grid North – taken from the National Grid System, this is a system of imaginary lines that divide your map into a series of squares.
Magnetic North – the point where a magnetic needle will align itself if freely suspended. The Earth has it’s own magnetic field. The Earth’s north & south magnetic poles do not coincide with the geographical poles – they are in fact 1200 miles apart!
Triangulation Points
Surveyors build up a map from a large number of triangles. The angles that are calculated from field work give accurate measurement on the ground.
The points from where this information is taken are called triangulation points (Trig Points).
These are small concrete pillars with a 3 channelled plate on top. On the map they are indicated by a blue triangle with a dot in the middle.
Scale & Scale
The scales of a map give you distances in nautical miles, statute miles & kilometres.
A nautical mile =6080 feet =1.85km
A statute mile =1760 yards =1,6093km
A kilometre =0.6214 mile or 5/8 of a mile
These scales are likely to be used by yourself when route planning.
Conventional Signs - Features
Always give the number along the bottom first.
Some people remember this by 'along the corridor and up the stairs' .
Find the square you want, find the Eastings (across) value for the left side of the square, and then find the Northings (up) value for the bottom of the square. Write down the numbers and you have a four figure grid reference. For example the letter A in the example below is 02 across and 51 up and therefore has the four figure grid reference is 0251.
6 Figure Grid References��Start by working out the basic four figure grid reference.
Then imagine the square is divided up into tenths.
You can do this by eye or more accurately using a ruler.
Using the example below the is in the square 0150, although more accurately it is 5 tenths across and 8 tenths up within the grid square 0150 and therefore has the six figure grid reference 017508.