# Equidistant Conic Projection — Standard

## Graticule

Meridians: Equally spaced straight lines converging to a common
point, usually beyond the pole. The angles between the meridians are
less than the true angles.

Parallels: Equally spaced concentric circular arcs centered
on the point of meridanal convergence.

Poles: Normally circular arcs, enclosing the same angle as the
displayed parallels.

Symmetry: About any meridian.

## Features

`eqdconicstd`

implements the Equidistant
Conic projection directly on a reference ellipsoid, consistent with
the industry-standard definition of this projection. See `eqdconic`

for
an alternative implementation based on rotating the rectifying sphere.

Scale is true along each meridian and the one or two selected
standard parallels. Scale is constant along any parallel. This projection
is free of distortion along the two standard parallels. Distortion
is constant along any other parallel. This projection provides a compromise
in distortion between conformal and equal-area conic projections,
of which it is neither.

## Parallels

The cone of projection has interesting limiting forms. If a
pole is selected as a single standard parallel, the cone is a plane,
and an Equidistant Azimuthal projection results. If two parallels
are chosen, not symmetric about the Equator, then an Equidistant Conic
projection results. If a pole is selected as one of the standard parallels,
then the projected pole is a point, otherwise the projected pole is
an arc. If the Equator is so chosen, the cone becomes a cylinder and
a Plate Carrée projection results. If two parallels equidistant
from the Equator are chosen as the standard parallels, an Equidistant
Cylindrical projection results. The default parallels are [15 75].

## Remarks

In a rudimentary form, this projection dates back to Claudius
Ptolemy, about A.D. 100. Improvements were developed by Johannes Ruysch
in 1508, Gerardus Mercator in the late 16th century, and Nicolas de
l'Isle in 1745. It is also known as the Simple Conic or Conic projection.

## Limitations

Longitude data greater than 135º east or west of the central
meridian is trimmed.

## Example

landareas = shaperead('landareas.shp','UseGeoCoords',true);
axesm ('eqdconicstd', 'Frame', 'on', 'Grid', 'on');
geoshow(landareas,'FaceColor',[1 1 .5],'EdgeColor',[.6 .6 .6]);
tissot;