Map skills: grid references, scale and direction
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लेसन नोट्स
Compass Points and Direction
- Compass points are used to describe direction on a map.
- The 8-point compass includes the four cardinal points (North, East, South, West) and the four intercardinal points (North-East, South-East, South-West, North-West).
- The 16-point compass adds intermediate points such as North-North-East, East-North-East, etc., allowing more precise direction descriptions.
- On a map, North is usually at the top, but always check the compass rose or north arrow.
- To give a direction from one place to another, identify the starting point and the destination, then state the compass direction between them.
Four-Figure Grid References
- A four-figure grid reference locates a square on a map to the nearest kilometre (or grid square).
- The reference is written as a two-digit easting followed by a two-digit northing (e.g., 23 45).
- Eastings are the vertical grid lines; they increase in value from left to right.
- Northings are the horizontal grid lines; they increase in value from bottom to top.
- Always read the easting first (along the corridor), then the northing (up the stairs).
Six-Figure Grid References
- A six-figure grid reference pinpoints a location more precisely within a grid square.
- It is written as a three-digit easting followed by a three-digit northing (e.g., 234 456).
- The first two digits of each part give the grid square; the third digit estimates tenths of the square.
- To find a six-figure reference, divide the grid square into 10 equal parts both horizontally and vertically.
- Six-figure references are useful for identifying exact features such as a building or a bridge.
Map Symbols and Keys
- Map symbols are small pictures or letters that represent real-world features on a map.
- A key (or legend) explains what each symbol means.
- Symbols are used to save space and make maps easier to read.
- Common symbols include blue lines for rivers, green areas for woodland, and black lines for roads.
- Always check the key before interpreting a map, as symbols can vary between different map series.
Scale: Linear and Ratio
- Scale shows the relationship between distance on a map and distance on the ground.
- A linear scale (or bar scale) is a line divided into segments that represent actual distances, such as kilometres.
- A ratio scale expresses the relationship as a ratio, e.g., 1:50 000, meaning 1 unit on the map equals 50 000 units on the ground.
- On a 1:50 000 map, 1 cm represents 0.5 km (or 1 km is represented by 2 cm).
- To measure a straight-line distance, use a ruler and convert using the scale.
- To measure a curved distance (e.g., along a road or river), use a piece of string or a map measurer, then convert using the scale.
Latitude and Longitude
- Latitude and longitude are coordinates used to locate places on the Earth's surface.
- Latitude lines run east-west and measure distance north or south of the Equator (0°).
- Longitude lines run north-south and measure distance east or west of the Prime Meridian (0°).
- Latitude and longitude are measured in degrees, minutes, and seconds.
- They form a geographic coordinate system (GCS) that is based on the three-dimensional shape of the Earth.
Map Projections and Coordinate Systems
- A map projection transforms the curved surface of the Earth onto a flat map.
- A projected coordinate system (also called a grid reference system) uses Cartesian coordinates (x, y) on a flat surface.
- In many systems, the x-coordinate is called the easting and the y-coordinate is called the northing.
- Examples of projected coordinate systems include the Universal Transverse Mercator (UTM) and the British National Grid.
- Projected coordinate systems are defined by a map projection, a geodetic datum, an origin point, and a unit of measure.
- Different projections distort the Earth's surface in different ways, so no single projection is perfect for all purposes.
Using Grid References and Scale Together
- Grid references and scale are often used together to describe locations and measure distances.
- First, locate the feature using a grid reference; then use the scale to measure distances to other features.
- For example, you can measure the distance between two grid references by using the scale on the map.
- When measuring distance, always ensure you use the correct unit (e.g., km or miles) as indicated by the scale.
स्लाइड्स
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प्रैक्टिस सवाल
फ्री प्रीव्यू — 58 में से 8 सवाल। सभी देखने के लिए साइन अप करें।
1.Which of these is a grid reference system used in the United Kingdom?
Easy- ABritish National Grid
- BState Plane Coordinate System
- CUniversal Transverse Mercator
- DMilitary Grid Reference System
2.In which decade was the State Plane Coordinate System developed in the United States?
Easy- A1920s
- B1930s
- C1940s
- D1950s
3.Why did the U.S. Army Map Service print grids on maps during World War II?
Medium- ATo make maps look more modern
- BTo help soldiers quickly and accurately measure and report their location
- CTo replace latitude and longitude entirely
- DTo confuse enemy forces
4.What does MGRS stand for?
Easy- AMilitary Grid Reference System
- BMap Grid Reference Standard
- CMilitary Geographic Reference System
- DMap Grid Resolution System
5.Which organisation developed the Universal Transverse Mercator coordinate system?
Medium- AThe British Ordnance Survey
- BThe German Wehrmacht
- CThe U.S. Army Map Service
- DThe United Nations
6.In which year was the first version of the British National Grid released?
Easy- A1918
- B1938
- C1945
- D1980
7.What was the main reason for creating the Military Grid Reference System (MGRS)?
Medium- ATo replace the Universal Transverse Mercator system
- BTo make UTM coordinates easier to communicate unambiguously
- CTo provide a system for civilian use only
- DTo align with political boundaries
8.Why did several countries create their own national grid systems after World War II?
Medium- ABecause UTM zones do not align with political boundaries
- BBecause UTM was too expensive
- CBecause they wanted to use different units of measure
- DBecause the United Nations required it
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