What is a secant conic projection?

The most simple Conic projection is tangent to the globe along a line of latitude. This line is called the standard parallel. The meridians are projected onto the conical surface, meeting at the apex, or point, of the cone. These projections are called Secant projections and are defined by two standard parallels.

What is a conic projection used for?

Distortion at the poles is so extreme that many maps that use conic projections remove the polar regions. Conic projections are typically used for mid-latitude zones with an east–west orientation. They are normally applied only to portions (such as North America or Europe ) of a hemisphere.

Does a secant projection intersect the Earth?

In the secant case the plane intersects the globe along a small circle forming a standard parallel which has true scale. The normal polar aspect yields parallels as concentric circles, and meridians projecting as straight lines from the center of the map.

How do you know if a projection is Tangentant or secant?

If the projection surface intersects the globe instead of merely touching its surface, the resulting projection is a secant rather than a tangent case. Whether the contact is tangent or secant, the contact points or lines are significant because they define locations of zero distortion.

What is Secant projection in GIS?

In map projections, the secant line is the line at which the developable surface of a conic or cylindrical projection “slices” through the sphere of the earth. This is opposed to a tangent line, where the developable surface only touches the sphere of the earth at one line.

What are developable surfaces GIS?

GIS Dictionary. developable surface. [map projections] A geometric shape such as a cone, cylinder, or plane that can be flattened without being distorted. Many map projections are classified in terms of these shapes.

What is developable surface in geography?

A developable surface is a geometric surface on which curved surface the earth is projected; the end result being what we know of as a map. Geometric forms that are commonly used as developable surfaces are planes, cylinders, cones, and mathematical surfaces.

What is the difference between a projection and distortion?

With projections the distortion is minimal at the lines of tangency, or the line along which the projection and the surface of the earth intersect. The further from those lines you get, the more distortion appears in the projection. Different projections are better at minimizing different typed of distortion.

What are the four standard types of projection?

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• Orthographic Projection. Orthographic projection shows a 3D object in two dimensions so that you can see three views: the front view, side view and top view.
• Axonometric Projection. Axonometric is another type of orthographic projection.
• Oblique Projection.
• Perspective Projection.

What are the three types of projections?

Three of these common types of map projections are cylindrical, conic, and azimuthal.

How does a Secant projection work?

Some map projections contact the earth’s surface along a point or line, called a tangent, while other map projections contact the earth’s surface along two lines, called secants. As you move farther away from the tangent or the secants in either a northerly or southerly direction, distortion increases.

Which is an example of a secant projection?

Secant Projections. As mentioned, when a conic or a cylindrical map projection surface is made secant, it intersects the ellipsoid, and the map is brought close to its surface. For example, the conic and cylindrical projections shown in the illustration cut through the ellipsoid.

What is the difference between a tangent and a secant?

Some map projections contact the earth’s surface along a point or line, called a tangent, while other map projections contact the earth’s surface along two lines, called secants. Both tangents and secants represent locations on the map projection where there is no distortion.

Which is better a conic projection or a tangent projection?

Conic projections. It is also possible to define a Secant projection by one standard parallel and a scale factor. The distortion pattern for Secant projections is different between the standard parallels than beyond them. Generally, a Secant projection has less overall distortion than a Tangent projection.

What are the characteristics of a Mercator projection map?

The line of contact between the earth and this surface is called a tangent. If there are two such lines, they are called secants. The contact point (or points) between the spheroidal earth’s surface and the plane of the map projection is the only location where the properties of the projection are true.