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John P. Snyder

Publications and source records attributed to John P. Snyder.

5 recordsLinked to original sources

“Magnifying-Glass” Azimuthal Map Projections

For maps focusing on a region of interest, but including surrounding areas to provide a setting, new azimuthal projections have been developed with a 'magnifying-glass' effect. On two such projections, inside a circle bounding the region of interest is a standard Azimuthal Equidistant or Lambert Azimuthal Equal-Area projection. Between this circle and an outer bounding circle azimuths remain true and the radial or area scale, respectively, remains constant, but at a reduced value. On four other projections, the inner portion is a standard azimuthal projection, which may be Stereographic, Gnomonic, or the above, but beyond this portion, the radial scale is gradually reduced to zero. Equivalents with rectangular boundaries are also available.

American Cartographer

New equal-area map projections for noncircular regions

A series of new equal-area map projections has been devised. Called Oblated Equal-Area, its lines of constant distortion follow approximately oval or rectangular paths instead of the circles of the Lambert Azimuthal Equal-Area projection or the straight lines of the Cylindrical Equal-Area projection. The projection series permits design of equal-area maps of oblong regions with less overall distortion of shape and scale than equal-area maps on other projections.

American Cartographer

EFFICIENT TRANSFER OF DATA BETWEEN MAPS OF DIFFERENT PROJECTIONS.

There are several ways to transfer data from an existing map to another map by computer. If the projection and parameters of both maps are known, analytic formulas may be used to convert rectangular coordinates of the first map to latitude and longitude and then to rectangular coordinates of the second map. This general solution, contained in a USGS computer program, involves inverse formulas for the first projection and forward formulas for the second projection.

Conference Paper

The modified polyconic projection for the IMW

The modified Polyconic map projection designed by Lallemand and adopted for the International Map of the World between 1909 and 1962 has two meridians and two parallels which are true to scale. Constructed geometrically in the past, forward and inverse coordinate transformations may be calculated analytically in order to transfer data from existing quadrangles to other maps. The equations for these transformations are derived and used to calculate representative tables of coordinates andscale factors. Although the projection is neither equal-area nor conformai, scale does not vary more than 0.06% throughout the quadrangle.

Cartographica: The International Journal for Geogr