- Reading a map is a language composed of lines, colors and symbols
- 5 basic colors are used for Topographic Maps:
- Brown (Contour Lines)
- Black (Man Made features such as Roads, Trails, Building)
- Blue (Water features such as stream, river)
- Green (Vegetation such as forest)
- Red (Highway and Land Grids)
- Pink, minor color (Build up area, civilization)
- Purple, minor color (Updated Map information)
- Symbols are used to represent the natural and man-made features of the eath
- Lines show relief (show differences in hight). It indicates variations in terrain features and heights of natural features.
- Every map has Margin Information about the map (kinda considered as Map instruction)
It is very important that we need to read Map instructruction here aka Margin Information where it is always at the bottom of Tropographic Map:
1- Map Legend: show the symbols of prominent natureal and mad-made objects on the ground.
I used to walk through Marsh or swarmp once during orienteering in VA and it was not fun.
2- Map Scale: give us the ratio of the distance on the map to the distance on the actual ground.
Above, Scale is shown as 1:50,000 meaning 1 inch on the map equals 50,000 inches on the actual ground. Or 1 meter on the map equals 50,000 meters on the ground. The larger the ratio, the less detail can be placed on the map. So the smaller radio means more detail on the map. E.g 1:25,000 will have more detail on it.
Military map is usually 1:50,000.
The right side tells you what unit measurement you want to use where as the left is always in meters so as seen here each alternative color dot line is 100m at the left so 5x of alternative dot line is 500m and 10x = 1000m
3- The declination diagram:
The 3 Norths
True North, Magnetic North, and Grid North
The declination diagram shows the 3 norths above on our map and it is very important to know how to convert Grid Noth Azimuth (Azimuth retreived after calculation on your map) to Magnetic North Azimuth (the Azimuth to be used on your compass) aka G-M angle.
For example below:
To convert from Grid Azimuth to Magetic Azimuth, you will have to ADD G-M angle which is 9 degree
E.g I found the azimuth on the map to my destination is 150 degree so to use it on my Compass, I will have to add it with 9 degree: 150 + 9 = 159 degree so I would dial my compass azimuth to 159 degree.
Note: Converting with GM angle that resulted in value greater than 360 degree or less than 0 degree.
- After converting G-M angle and resulted in greater than 360, what should we do?
E.g: Grid Azimuth is 357 degree + 9 degree to convert to Magnetic Azimuth = 366 degree (note that on the compass there is only 0 degree to 360 degree) so in this case we will have to substract it with 360: 366 – 360 = 6 degree magnetic so I would dial 6 degree on my compass.
- After converting G-M angle and resulted in less than 0, what should we do?
E.g Grid Azimuth is 5 degree and the G-M angle on the map is -12 so converting it to Magnetic Azimuth: 5 + (-12) = -7 (note that on the compass there is only 0 degree to 360 degree) so in this case we will have to add it with 360: -7 + 360 = 353 degree magnetic so I would dial 353 degree on my compass.
Additional information:
Too detail but point to remember is right to left = ADD and left to right = substract but usually Map margin would tell you whether to ADD to substract based on the conversion you are using either G to M or M to G (G: Grid, M: Magnetic).
Tip: you either look at the map margin to know your map scale so you can know which Triangle in your protractor (scale) would be used to plot your point on the map or just put each triangle on the map grid and if it fits the map grid, it is to be used. Ploting point on the map is easy and if you are a soldier you would be expect to know how to do it. Rule of thumb when ploting a poing: the point is plotted from left to right and down to up direction per the grid points.