# PA/DEL border question
**URL:** https://boards.straightdope.com/t/pa-del-border-question/82089
**Category:** Factual Questions
**Created:** [September 17, 2001, 4:21am UTC](https://boards.straightdope.com/t/pa-del-border-question/82089 "2001-09-17T04:21:21Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)
#### Post date: [September 17, 2001, 4:21am UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/1 "2001-09-17T04:21:21Z")
Part of the border between Pennsylvania and Delaware is a
circular arc. Where is the center for this circle, and what is its significance?
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### Author:  [@tomndebb](https://boards.straightdope.com/u/tomndebb)
#### Post date: [September 17, 2001, 4:57am UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/2 "2001-09-17T04:57:50Z")
According to [This site discussing the Mason-Dixon Line](http://freespace.virgin.net/john.cletheroe/usa_can/usa/mas_dix.htm) it is called the 12-Mile Arc:
> [@](#):
>
> The Delaware/Pennsylvania border extends in an easterly direction for about a mile from the point where Delaware, Maryland and Pennsylvania meet. It then follows a circular arc which extends around the north of Wilmington to the Delaware River. This arc is centred on the dome of the courthouse in the town of New Castle, which is a few miles south of Wilmington. Since the arc has a radius of twelve miles it is known as the Twelve Mile Arc. The twelve mile arc was not part of the original Mason-Dixon Line as surveyed by Mason and Dixon but its history is interesting nevertheless.
Go to the site and scroll down to the section labeled
> [@](#):
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> The Delaware/Pennsylvania Border - The Twelve Mile Arc
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### Author:  [@Wonko\_The\_Sane](https://boards.straightdope.com/u/Wonko_The_Sane)
#### Post date: [September 17, 2001, 9:04pm UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/3 "2001-09-17T21:04:29Z")
Thanks! I used to live there, and I always wondered about that.
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### Author:  [@evilhanz](https://boards.straightdope.com/u/evilhanz)
#### Post date: [September 17, 2001, 9:30pm UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/4 "2001-09-17T21:30:50Z")
Hmmm. Are there any other circular borders in the world? That is, a border designed to form an arc of some significant portion of a circle’s circumference? (Not just borders which appear semicircular)
Perhaps this merits its own thread …
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### Author:  [@fandango](https://boards.straightdope.com/u/fandango)
#### Post date: [September 24, 2001, 6:02pm UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/5 "2001-09-24T18:02:02Z")
> [@](#):
>
> \*Originally posted by evilhanz \*
> \*\*Hmmm. Are there any other circular borders in the world? That is, a border designed to form an arc of some significant portion of a circle’s circumference? (Not just borders which appear semicircular)
Any border decided by latitude, i.e. the majority of the US/Canada border is based on a circle’s circumference (when seen from the north pole).
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### Author:  [@evilhanz](https://boards.straightdope.com/u/evilhanz)
#### Post date: [September 24, 2001, 6:12pm UTC](https://boards.straightdope.com/t/pa-del-border-question/82089/6 "2001-09-24T18:12:48Z")
fandago - Clever. However, on a standard projection, those borders appear to be straight lines. I was interested in demarcations which are similar to the PA/DE border discussed above when viewed on a standard projection.
I should have been more specific in my followup question to avoid the smart alecs 😉