A Map, A Map, My Kingdom for a Map (and NOT those things showing up in papers)

What is wrong with this figure?

No, its not the color scale or using t’ for elevation (though, um, why t’ anyways?).  It is that this is not a map*.  This is what GG has always called a “computer-stupid” map projection.  Why? Look at the axes.  Since when is one degree of latitude equal to one degree of longitude at 40°N? Look, twenty or thirty years ago you might have had an excuse.  Today? No. None. Nada.  Not in the age of Generic Mapping Tools or the geographic toolbox in Matlab. You could at least make a computer-stupid Mercator (that is where you simply squish the horizontal axes to approximate the latitude:longitude ratio at some point in the map; a true Mercator has a varying latitude scale). Look, maps are useful when done right.  In this case, you probably want to preserve area, so you look for an equal-area projection (there are lots).  In some cases (e.g., SKS split maps), you probably want to preserve angles, so you might opt for the Mercator. This map (and its many cousins in this paper) preserves nothing.  Distance scales depend on what direction you are measuring, angles do not correspond to angles on the earth, area is not preserved–in short, there is absolutely nothing good to say about this. Now this is far from the only paper GG has seen with this failing, but this has got to stop (just like the insane inability to properly cite the literature). All geoscientists should be able to make a map. This is, to the Grumpy Geophysicist, a demonstration of profound inability to get the simple things right, and if you don’t get the simple things right, why believe anything else in the paper?

A partial apology: In choosing this map to act as a stand-in for GG’s rant (which, on a broad scale, he stands behind), it appears (see comments below) GG chose an example where this projection was consciously chosen–why, GG cannot figure, but as there was a deliberate reason, the innuendo in the text above is misguided.  So apologies to Thorsten Becker: that last sentence should not be construed as condemning that particular paper.  But GG still hates this projection.

*OK, GG is wrong.  It is a map and a named projection, as Thorsten kindly pointed out below.

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6 responses to “A Map, A Map, My Kingdom for a Map (and NOT those things showing up in papers)”

  1. Thorsten Becker says :

    Unlike what seems to be implied, I happen to realize that we live on an ellipsoid, and have taught map projections for more than a decade. Shocks, I still like the cylindrical equidistant projection, at times, such as for this application, since there is no particular reason to preserve area nor angle, every projection is necessarily imperfect, and most readers appear aware of this fact. I choose my projections guided by how I think information is best conveyed, case by case, even if it may offend the churches of Hammer and Mercator.

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  2. cjonescu says :

    So this was a conscious choice for you? Well, OK, though GG seems no benefit to it whatsoever (why not preserve area in this case? The integrated area is related to the total load and allows somewhat better comparisons of the scale length of the anomalies at different latitudes). In the past and in other situations, it was a lazy projection enabled by simple raster plotting routines (GG could name particulars, but is trying to minimize pissing off more than one person a week). Hence GG’s appellation of “computer stupid,” which is apparently incorrect in this instance as it was a deliberate choice. Most of the continued use of this projection is in fact to display raster sets gridded to lat/lon so that every pixel is equally represented.

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  3. cjonescu says :

    An addendum if anybody comes along later. The USGS volume on map projections (Bulletin 1532, Professional Paper 1395–p. 90-1) “While the Equidistant Cylindrical projection has received limited use by the USGS and generally has limited value, it is probably the simplest of all map projections to construct and one of the oldest….The USGS uses the Equidistant Cylindrical projection for index maps of the conterminous United States, with insets of Alaska, Hawaii, and various islands on the same projection…. Neither the scale nor the projection is marked [on these maps], to avoid implying that the maps are suitable for normal geographic information….The projection was chosen largely for ease in computerized plotting. ” It would seem a map unsuitable for normal geographic information would be a really lousy map.

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