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"In practical terms" usually means choosing a limit on how small a kink must be to avoid being ignored. Unfortunately, this resolution is rarely mentioned, even though it is assumed in and significantly affects the measurement. I suppose cartographers have some default that they work to. —Quondum16:25, 3 August 2014 (UTC)[reply]
For seacoasts I imagine using the shortest path lying between average low– and high-tide contours. The land boundaries of the US are defined as straight lines between markers. —Tamfang (talk) 22:56, 4 August 2014 (UTC)[reply]
Here's a helpful graphic I ran across from our article on Surveying: "How a surveyor used both traverse and offset measurements to record the location of a shoreline (blue). The circles are rods driven into the ground to create reference points. Dashed lines are traverse lines where the surveyor has recorded whole circle bearings (Azimuths) and distances that allow the reference points' position to be plotted on a map. The red lines are offset measurements." El duderino(abides)05:36, 8 August 2014 (UTC)[reply]
Can a number of the form 7n+2 (for positive integer n) be prime? If not, why not? Many numbers of the general form an+b are prime, but a quick search using PARI/GP does not find any primes of the form 7n+2 for small n, so I wonder whether a number of this form can even be prime at all. -- ToshioYamaguchi09:29, 3 August 2014 (UTC)[reply]
This sounds like a homework question from the first week of a number theory course, so I'll just give you a hint: consider numbers of the form 3x+1... RomanSpa (talk) 12:09, 3 August 2014 (UTC)[reply]
Well, it's not a homework question, I am just doing this for my own amusement (which of course you can believe or not). I am not sure I understand the hint you give, but a quick check appears to imply that all of these numbers are divisible by 3. -- ToshioYamaguchi12:50, 3 August 2014 (UTC)[reply]
I often use PARI/GP to quickly test some numbers for small factors to look for a pattern. This easily adaptable example tests for the first 25 primes as factors in your sequence:
The answer will often be obvious from such output, although you may need a little knowledge of modular arithmetic if you want a complete proof. PrimeHunter (talk) 15:05, 3 August 2014 (UTC)[reply]