Which word is more appropriate in a geographical mapping context when referring to counties in a state, contiguous states within a country, contiguous countries within a continent, etc?

Are they interchangeable? Based on this n-gram 'coterminous' is more common, though 'conterminous' seems more accurate?


  • having the same border or covering the same area
  • being the same in extent; coextensive in range or scope


  • having a common boundary; bordering; contiguous
  • meeting at the ends; without an intervening gap

The set of all counties would be coterminous with the state as a whole, occupying the same area.

One county would be conterminous with a neighboring county, having a common border.


Good question. TBH, I'm not sure why, in both cases, it isn't in latin declension? (just "us" not "ous" -- greek?)

**Edit - leaving parenthetical up. upon reflection, i think -us still noun, -ous, latin not greek, more at adjective. hence ous (edited below).

Termin - at end, final, limit (airport terminal, exterminate)

co - together, with, group (coordinate, coevolve)

con - with (more at synchronized; contemporary, con(n)ect, convey)

coterminous - ending at the same time (independent)

The procedures are coterminus

conterminous - just seems wrong (maybe thats why it's used less). ending together (at mutual)

**Edit (pt2) - con + terminus (con, think: Spanish). With ending (contra: cliffhanger). "The plot is conterminous" - but this is wrong, i think heh?*

As per your question - why doesn't contiguous work? If you mean "all the states of the union," why not constituent?

And then there's the n-gram graph, from your source

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    I've never come across "conterminous"; my preference would be for "coterminous"; but I note that the Online Etymological Dictionary mentions that "coterminous" or "co-terminous" are "malformed in English" from Latin roots, and that "Latin purists prefer conterminous." – tautophile Jul 21 '18 at 4:02
  • example: sciencedirect.com/science/article/pii/S0034425709002545 Now I'm wondering if one is used more often in an academic context. Here I believe it's referring to the lower 48 states. – Donald Peat Jul 21 '18 at 5:03
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    @tautophile Latin purists remain mute spectators as writers prefer to save a letter. See the nGram! – Kris Jul 23 '18 at 6:23
  • @Kris yes I thought more about it over the weekend and have updated my answer... – tidbertum Jul 23 '18 at 14:05

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