My wife gave me the book by Monmonier for Christmas - she likes to try and find things not on my list if she can. It's a solid book, one that you pick up to get a Cartography 101 course. There were things I knew about maps just from frequent use that I didn't know the names for, and close definitions usually give you quick, improved understanding of what you learned informally. So I'm sailing through the first 40 pages happily, even though there aren't many of the fascinating anecdotes one hopes to get from a book with such a title. Mildly challenging, head-nodding "yep...yep..." sort of stuff.
On page 41 he shows me something I have never noticed, but instantly recognise as a way to lie with maps that can be powerful: the ranges in the legend. Such as this one, which I came across a day later. (Click to enlarge)
By Bill Rankin — Citynoise (talk • contribs) - Own work, CC BY-SA 3.0, Link
I almost missed this, following my little information trail after Grim mentioned the general topic. Just as I was about to click off I checked the population density legend and saw, by golly, exactly what Monmonier had written about. Those are curious adjoining ranges in there.
Less than 150
I don't say they are wrong or deceitful. They may be the cartographer's best compromise to illustrate density. For all I know, those ranges may be a common convention used worldwide. The downward track in the later ranges, 200%...167%...150% seems sensible, as do the Less than/Over cutoffs. Other numbers might have told the story as well, but these do the job. If "less than 250" had been chosen for the first color, then the second would be 300% higher, fitting the trend above. Perhaps Rankin though it important to add that extra level of distinction at the lowest level. One of Monmonier's repeated points is that all maps lie, because they have to suppress some information in order to highlight other information.
Yet I had unconsciously assumed the legend marked some regular interval. Bad assumption, even with honorable, skilled cartographers. Cue Batman: "Imagine what this weapon could do if it fell into the wrong hands, Robin."
Additional notes: The only other map with NE at the top is the Appalachian Trail map, which covers an expanded version of this area. The 45-degree difference really does show the terrain and city connections differently. Another way to "lie" with a map, by telling a more important truth.