# 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.

## Man-made vertical obstruction

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

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

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 =+ 250ft. Sum vertical error and elevation = 6715 ft. Round to next higher 100 ft. level = 6800 ft. Maximum Elevation Figure (MEF) = 6^{8}

## 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:

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

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 =+ 250ft. Sum elevation, allowance, vertical error = 10565 ft. Round to next higher 100 ft. level = 10600 ft. Maximum Elevation Figure (MEF) = 10^{6}

## 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:

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

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 =+ 250ft. Sum elevation, allowance, vertical error = 300 ft. (Even hundred - do not round) = 300 ft. Maximum Elevation Figure (MEF) = 0^{3}