# Educational program on the map projection with pictures Bashny.Net

Data visualization of all kinds, having a certain geographical distribution, has recently become more and more widespread. Here, Habré, articles with maps found almost every week. Maps in the articles are very different, but one thing unites them: as a rule, they use only two map projections, though - not the most successful of the existing ones. I would like to give a few illustrative examples of the projections, which look more aesthetically pleasing and better suited for different kinds of visualization. This article will address global projection and the projection of most of the land, as the visualization of something on a map of the world, perhaps, is the most common of these problems.

#### Options solutions h4> What to do with the global data, if we for some reason needed a projection, it is better to retain such properties of objects, as a form, area, distances and angles? The laws of geometry do not allow us to keep all of these properties at once, expanding the circular surface of the Earth on a plane. However, data visualization is most important aesthetics and perception, rather than the preservation of properties, both for navigation and measurement tasks. Because it becomes possible to select a projection distortions which are evenly distributed properties. And these projections, there are quite a few. There are three most famous having similar properties, "Triple Winkel» Winkel Tripel WKID: 54042 PROJ.4: wintri i>, «Robinson projection» Robinson projection WKID: 54030 PROJ.4: robin < / i>, «projection Kavraiskii» (Kavrayskiy projection). The first and last are visually minimal distortion and non-specialist without seeing a degree grid, generally it is difficult to distinguish them, because I will give an illustration for the Winkel Tripel, like the one that I personally like best. That's the description of this projection looks format ESRI WKT:

``` ``` PROJCS [& quot; Robinson & quot ;, GEOGCS [& quot; GCS_WGS_1984 & quot ;, DATUM [& quot; D_WGS84 & quot ;, SPHEROID [& quot; WGS84 & quot ;, 6378137, 298.257223563]], PRIMEM [& quot; Greenwich & quot ; 0], UNIT [& quot; Degree & quot ;, 0.017453292519943295]], PROJECTION [& quot; Robinson & quot;], PARAMETER [& quot; central_meridian & quot ;, 0], PARAMETER [& quot; false_easting & quot ;, 0], PARAMETER [& quot; false_northing & quot; , 0], UNIT [& quot; Meter & quot ;, 1]]  code>  pre>

As is easily seen, although the distortion circuits and some increase in area of ​​the poles are also observed, but it can not be compared with stretching geographic projection and a proportional increase in the Mercator projection.

Here it is necessary to digress and note that the form of this projection, the default is suffering disadvantage, which applies to other global projections. The fact is that if for the central meridian - the line connecting the north and south pole through the center of the map (longitude of origin) - take the prime meridian, the map will be cut by 180 mu. But with a third of Chukotka is on the left edge of the map, and two-thirds - on the right. To make the map more beautiful section must be held somewhere in the area of ​​169 th meridian east of the western islands Ratmanova, which for central should be taken 11 minutes. Here's an illustration of what happens:

But changes to the description of this case in ESRI WKT:
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``````  PROJCS [& quot; Robinson & quot ;, GEOGCS [& quot; GCS_WGS_1984 & quot ;, DATUM [& quot; D_WGS84 & quot ;, SPHEROID [& quot; WGS84 & quot ;, 6378137, 298.257223563]], PRIMEM [& quot; Greenwich & quot ; 0], UNIT [& quot; Degree & quot ;, 0.017453292519943295]], PROJECTION [& quot; Robinson & quot;], PARAMETER [& quot; central_meridian & quot ;, 11], PARAMETER [& quot; false_easting & quot ;, 0], PARAMETER [& quot; false_northing & quot; , 0], UNIT [& quot; Meter & quot ;, 1]]  code>  pre>

In the format of the definition of the coordinate system for longitude PROJ.4 projection center is specified by  + lon_0 =.  I>

11th meridian - "magic" number: almost all the world of projection, having uniform scale along the equator, can be cut according to the Bering Strait, for if it is to take a central and not a zero.

Note that having to choose the projection, not take into account all the existing real requirements for visualization. For example, if the data relate to the climate, it may make sense to map a line of latitude, or use a projection of where they are horizontal and not bent to the edges of the card (ie, abandon Triple Winkel in favor of, for example, Robinson). In this case, it will easily and accurately estimate the relative proximity of different locations for the poles and equator. Another significant plus Robinson projection - the fact that it is supported by a plurality of software, including the open, while about some of the other can not be said.

Sometimes when you want to preserve some property, for example - the ratio of the object area (countries) - aesthetic side suffers. But since it still can for something needed, I will give one example of such a projection - "projection Mollveyde», Mollweide projection  WKID: 54009 PROJ.4: moll  i>.

As can be seen, it is quite reminiscent of the Robinson projection, but with the difference that the pole is still contracted to a point, from which form the polar regions looks highly distorted. But the proportion of the country's area, as required, saved a lot better.

The youngest competitor of these projections is the projection of the Natural Earth  PROJ.4: natearth  i> - it is a hybrid projection Kavraiskii and Robinson, and its parameters were selected group of American, Swiss and Slovenian experts in 2007, while age of most map projections - at least half a century.

For reprojection data into it there are a number of tools that have been written specifically for this, but its support is far from universal.

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