Map Coordinates for Dummies

Different map projections

One of the founders of the Antisocial Network spent many years working with mapping software, which is completely dependent on location data provided in map coordinates. That's probably why he's always giving the staff links to botched map information at the DotD award meetings. Today he gets his wish, as we feature Scott Thompson of Sciencing.com (again) for the inane post, "How do Map Coordinates Work."¹

Thompson, as is so often the case with people unfamiliar with maps, informs his readers that there are two kinds of map coordinates:

"Map coordinates are usually based on the system of latitude and longitude, which was first recorded by the astronomer Ptolemy in 150 CE. Another coordinate system that is widely used is the Universal Transverse Mercator system, or UTM. Part of reading a map or even a GPS device is knowing which coordinate system is being used."

We humbly submit that anyone unable to tell the difference between lat-long coordinates and UTMs deserves to get lost: it's Darwinian! That being said, we don't think that Thompson's devoting half his post to the lat-long system is a good use of space, mostly because lat-long is a geographic coordinate system, not a map coordinate system. Map coordinate systems are based on map projections, a term Thompson studiously avoids (probably because he has no idea what it is). Whatever...

Unfortunately, in his rush to the bottom of the page and his fifteen-dollar check, Scott had a few goofs. To wit,

• "One minute is 1.15 miles or 1.85 km on land, or 1 nautical mile..." wording that suggests that a minute of latitude is a different length on land than over water. Bad writing for a self-described "professional."
• Of longitude, he says, "This means that the degrees and minutes are not a constant measurement as they are with latitude..." a poor way to express that the horizontal distance represented by a degree of longitude varies with distance from the equator.
• Of UTM coordinates, Thompson claims that "The locations on the map grid are measured in meters... from a point to the west of the map..." which is incorrect: UTMs are measured from a line of longitude at the center of the UTM zone -- not "a point to the west." Perhaps Scott was confused by the notion of false easting, a large number (500,000) added to the east-west UTM coordinate to ensure that it is never a negative number.

• We have no idea where he came up with this bull: "...every grid on the map is eight degrees in height and six in width..." True, each UTM zone is six degrees wide, but a) that's not a grid on the map" and b) what's this 8 degrees high bullroar?
• And finally, Thompson mentions all the dozens of other map projections when he says that your map "may also use... some other less common coordinate system..." Well, Scott, we hate to disabuse you but UTM coordinates are the bastard stepchild of mapping: almost every other map uses a different projection (what you call a "coordinate system"), because the UTM projection makes lousy maps compared to a projection that is tailored to the location.

Worst of all, Thompson does little more than define a couple of location systems. He says nothing at all about how map coordinates work, which was, after all, the point of the OQ; no mention of grid coordinates, easting, northing, or even the word "projection." Anyone who knows more about maps than "how to find north" will understand why Thompson is receiving another Dumbass of the Day award for this claptrap. ¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was sciencing.com/map-coordinates-work-10022611.html

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