Pitney Bowes MapInfo Professional - Manual (Page 401)

recessing the cylinder into the earth so that it has two lines of intersection. Scale is true along these lines
of intersection.
You may see the scale factor expressed as a ratio, such as 1:25000. In this case it is generally called
the scale reduction. The relationship between scale factor and scale reduction is:
scale factor = 1-scale reduction
In this case the scale factor would be 1-(1/25000) or 0.99996.
False Easting and False Northing
As you can see in the Longitude/Latitude Projection Map , X and Y coordinate parameters are commonly
designated in relationship to a single point. Points to the left of that center point are negative and points
to the right are positive. Points above that center point are positive and points below that point are
negative.
In the days of the tall ships, these calculations and computations were done by hand. Using positive and
negative signs made these calculations more complicated. The terms "false easting" and "false northing"
were used to remove these signs and refer to the absolute value of the X and Y coordinates. MapInfo
Professional handles these computations, but these parameters still have to be accounted for in the
projections that use them.
Range (Azimuthal Projections)
The range specifies, in degrees, how much of the Earth is visible. The range can be between 1 and 180.
When you specify 90, you see a hemisphere. When you specify 180 you see the whole earth, though
much of it is very distorted.
About Polyconic Coordinate Systems
The following description has been copied from "Map Projections - A Working Manual", USGS Professional
Paper 1395, by John P. Snyder.
The Polyconic projection, usually called the American Polyconic in Europe, achieved its name because
the curvature of the circular arc for each parallel on the map is the same as it would be following the
unrolling of a cone which had been wrapped around the globe tangent to the particular parallel of latitude,
with the parallel traced onto the cone. Thus, there are many ("poly-") cones involved, rather than the
single cone of each regular conic projection.
The Polyconic projection is neither equal-area nor conformal. Along the central meridian, however, it is
both distortion free and true to scale. Each parallel is true to scale, but the meridians are lengthened by
various amounts to cross each parallel at the correct position along the parallel, so that no parallel is
standard in the sense of having conformality (or correct angles), except at the central meridian. Near
the central meridian, distortion is extremely small.
This projection is not intended for mapping large areas. The conversion algorithms used break down
when mapping wide longitude ranges. For example, WORLD.TAB, from the sample data shipped with
MapInfo Professional, may exhibit anomalies if reprojected using Polyconic.
Examples of Projection Entries in the MAPINFOW.PRJ File
The MAPINFOW.PRJ file lists the parameters for each coordinate system on a separate line, as in the
following examples:
"Mollweide (Equal Area)", 13, 62, 7, 0
"Albers Equal-Area Conic (Alaska)", 9, 63, 7, -154, 50, 55, 65, 0, 0
401 MapInfo Professional User Guide
Chapter 15: Working with Coordinate Systems and Projections