How many map projections are there

The north-south axis of every ellipse is the same length, however. This shows that distances are true-to-scale along every meridian; in other words, the property of equidistance on this map projection is preserved from the two poles. Azimuthal projections preserve directions azimuths from one or two points to all other points on the map. Gnomonic projections , like the one above, display all great circles as straight lines. A great circle is the most direct path between two locations across the surface of the globe.

See how the ellipses plotted on the gnomonic projection shown above vary in both size and shape, but are all oriented toward the center of the projection. In this example, that is the one point at which directions measured on the globe are not distorted on the projected graticule. This is a good projection for uses like plotting airline connections from one airport to all others. Some map projections preserve none of the properties described above, but instead seek a compromise that minimizes distortion of all kinds.

The example shown above is the Polyconic projection, where parallels are all non-concentric circular arcs, except for a straight equator, and the centers of these circles lie along a central axis.

The U. Geological Survey used the polyconic projection for many years as the basis of its topographic quadrangle map series until the conformal Transverse Mercator succeeded it. Another example is the Robinson projection, which is often used for small-scale thematic maps of the world it was used as the primary world map projection by the National Geographic Society from , then replaced with another compromise projection, the Winkel Tripel; thus, the latter has become common in textbooks.

Flex Projector is a free, open source software program developed in Java that supports many more projections and variable parameters than the Interactive Album. You can download Flex Projector from FlexProjector. Those who wish to explore map projections in greater depth than is possible in this course might wish to visit an informative page published by the International Institute for Geo-Information Science and Earth Observation Netherlands , which is known by the legacy acronym ITC.

The page is available at Kartoweb Map Projections. Registered Penn State students should return now take the self-assessment quiz about the Map Projections. You may take practice quizzes as many times as you wish.

They are not scored and do not affect your grade in any way. Skip to main content. Print Latitude and longitude coordinates specify positions in a spherical grid called the graticule that approximates the more-or-less spherical Earth. We often talk about map projections in terms of the ways in which they distort or preserve certain things about the Earth, which we call projection properties.

There are four main properties:. Notice how Greenland is about as big as South America on a Mercator projection. In reality, South America is eight times larger than Greenland. Notice here how Greenland looks the right size as compared to South America.

Projections which preserve areas are called equivalent or equal-area projections. A map projection either preserves areas everywhere, or distorts it everywhere. This is an all-or-nothing property. On the projection above, look at how Australia, on the right, is unrecognizable, and New Zealand is stretched out into a ring around the left edge of the map.

It stretches or twists or squashes them, instead. Contrast that with a Lambert Conformal Conic below , on the other hand, which preserves the general form of the landmasses.

Projections like this are called conformal projections. Under the hood, this property is actually a little more complex: comformal projections actually preserve local angles. But what that boils down to for cartographers is that places look more like themselves. In the example below, Greenland is shown as it appears on three conformal projections top row and three non-conformal projections bottom row. Notice how the conformal projections keep Greenland looking Greenlandy.

On the other hand, the Azimuthal Equidistant projection shows distances in the correct proportion. There are only projections that let you preserve distances relative to just one or two points on the map. Distances to and from the center of an Azimuthal Equidistant map are shown correctly, but distances between any other two points are distorted.

To identify individual features or locations distances are first measured from the west to the feature and then measured from the south to the feature. The three are combined to give a precise location — based on the map grid.

This is a mathematically simple projection. It is also an ancient projection possibly developed by Marinus of Tyre in Because of its simplicity it was commonly used in the past before computers allowed for very complex calculations and it has been adopted as the projection of choice for use in computer mapping applications — notably Geographic Information Systems GIS and on web pages. Also, again because of its simplicity, it is equally able to be used with world and regional maps.

In GIS operations this projection is commonly referred to as Geographicals. This is a cylindrical projection, with the Equator as its Standard Parallel. The difference with this projection is that the latitude and longitude lines intersect to form regularly sized squares. By way of comparison, in the Mercator and Robinson projections they form irregularly sized rectangles.

Refer to the section on Projections for more information about distortions generated by projections. Enter your Keywords. Commonly Used Map Projections. Breadcrumb Home Fundamentals of Mapping Projections. These are two examples of maps using Stereographic projection over polar areas.

In these the radiating lines are Great Circles. Produced Using G. In this the Great Circles are not as obvious as with the two Polar maps above, but the same principle applies: any straight line which runs through the centre point is a Great Circle. This is an example of how a Great Circle does not have to be a set line of Longitude of Latitude.

These two maps highlight the importance of selecting your Standard Parallel s carefully. For the first one the Standard Parallels are in the North and for the second they are in the South. Pseudoconic Projections are projections with parallels which are circular arcs with common central points. Unlike conic projections, the meridian is not constrained to be a straight line.

Examples of pseudoconic projections include "bonne", which is an equal-area map projection. The maps are not constrained to rectangles or discs. Pseudoconic projection is one of the oldest map types and although they were used by Ptolemy, they are seldom seen today. Map projections without distortions would represent the correct distance, direction, shapes, and areas on a map.

However, map projections have distortions which depend largely on the size of the area being mapped. Scale distortions on maps are shown on the map by an ellipse of distortion or using scale factor which is the ratio of the scale at a given point to the true scale.

Distortions on maps of countries or cities are not evident to the eye and can only be identified when computing distances and areas.