# How maximum elevation figures are calculated for a Tactical Pilotage Chart

The Calculate Maximum Elevation Figures tool computes the maximum elevation figures for a Tactical Pilotage Chart (TPC) based on the type of the highest vertical obstruction in a quadrangle. Two obstruction types influence the calculation: man-made and natural terrain. The calculation differs if one type is higher than the other or if the obstruction is below sea level.

If the highest vertical obstruction within a quadrangle is a man-made feature, the Calculate Maximum Elevation Figures tool follows this process:

1. Determine the elevation of the top of the feature (above mean sea level (MSL)).
2. Add the vertical error figure (vertical accuracy factor of data/source).
3. Round the resultant sum to the next higher hundred-foot level for the final figure. Note:

The resultant figure is not rounded up to the next higher hundred-foot level when it is an even multiple of 100.

### Example

```Elevation of Vertical Obstruction (top, above mean sea level)  =  6265 ft.
Possible vertical error                                        = + 250 ft.
Sum vertical error and elevation                               =  6715 ft.
Round to next higher 100 ft. level                             =  6800 ft.
Maximum Elevation Figure (MEF)                                 =    68```

## Natural terrain feature vertical obstruction

If the highest vertical obstruction within a quadrangle is a natural terrain elevation, the Calculate Maximum Elevation Figures tool follows this process:

1. Determine the highest natural terrain elevation.
2. Add an allowance of 61m (200 feet) for nonrepresented natural or man-made features.
3. Add the vertical error figure (vertical accuracy factor of data/source).
4. Round the resultant sum to the next higher hundred-foot level for the final figure. Note:

A resultant figure is not rounded up to the next higher hundred-foot level when the addition results in an even multiple of 100.

### Example

```Highest natural terrain elevation (above mean sea level)       =  10115 ft.
Allowance                                                      =    200 ft.
Possible vertical error                                        =  + 250 ft.
Sum elevation, allowance, vertical error                       =  10565 ft.
Round to next higher 100 ft. level                             =  10600 ft.
Maximum Elevation Figure (MEF)                                 =    106```

## Highest feature is below sea level

If the highest vertical obstruction within a quadrangle is below sea level (BSL), the Calculate Maximum Elevation Figures tool follows this process:

1. Add the BSL value to the 61m (200 feet) allowance, for nonrepresented natural or man-made features.
2. Add the vertical error figure (vertical accuracy factor of data/source).
3. Round the resultant sum to the next higher hundred-foot level for the final figure. Note:

A resultant figure is not rounded up to the next higher hundred-foot level when it is an even multiple of 100.

### Example

```Highest terrain elevation (above mean sea level)               =  - 150 ft.
Allowance                                                      =    200 ft.
Possible vertical error                                        =  + 250 ft.
Sum elevation, allowance, vertical error                       =    300 ft.
(Even hundred - do not round)                                  =    300 ft.
Maximum Elevation Figure (MEF)                                 =     03```

5/4/2011
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