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Frequently Asked Questions - Mountain High Maps

Q: What is the map projection formula for the Gall World Map?

A: The formula for the Pseudocylindrical Projection for the Gall 604 and 605 in the Mountain High Maps collection is given below:

R = Radius of the sphere at the scale of the map.

x = rectangular coordinate; distance to the right of the vertical line (Y axis) passing through the origin (if negative, it is distance to the left).

y = rectangular coordinate; distance above the horizontal line (X axis) passing through the origin (if negative, it is below).

= longitude east of Greenwich (for longitude west of Greenwich, a minus sign is used).

= longitude east of Greenwich of the central meridian of the map or of the origin of the rectangular coordinates (for west longitude, a minus sign is used). If is a pole, is the longitude of the meridian extending down on the map from the North Pole or up from the South Pole. On an interrupted projection, is the central meridian of each section.

= north latitude (if latitude is south, a minus sign is used).

Note 1: The latitudes and longitudes need to be converted from the degree system to the radian system - formula for this conversion is: radians = degrees * (2*Pi / 360).

Note 2: On map #604 Gall World, the radius has been calculated as 540.76 pixels.

Before using the above formula, either version of the World Gall map, #604 or #605, should be trimmed using the Graticule mask - this will give you the correct trim points on the East and West edges of the map, removing the excess overlap provided on these maps.

Further details can be found in "An Album of Map Projections" by John P. Snyder and Philip M. Voxland, published by the U.S. Geological Survey (Professional Paper 1453).


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