The polyconic projection (see fig. 5) is used for most Government maps.
The polyconic projection is not used for very extensive areas of the earth's surface, as for instance a hemisphere.
These conditions are substantially fulfilled by several projections, of which the polyconic is used in the United States.
So far the construction is the same for both forms of polyconic.
On polyconic and other larger scale charts distances are measured from the scales printed on the chart.
