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Question for cartographers

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Feb 18, 2020 - 9:25:51 PM
3905 posts since 10/18/2007

I'v never understood how they determine the length of coastlines. For instance, a state in the US might brag that it has 544 miles of ocean coastline. But how is that measured? From what perspective or height? The coast of Oregon would look fairly straight if the camera is located 1000 miles above the coast. But if the camera is only 1 mile above the coast there would be many little inlets and promontories that might be measured. From just 100 feet up the shore would be appear crooked, especially in rocky areas, and therefore would yield a lot more distance to the estimated length of land touching the water. I suspect an extreme close-up--say, at the molecular level--of the entire coast of the state might yield many, many thousands of miles of coastline. Just wondering.

Feb 18, 2020 - 10:36:04 PM
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Chris Meakin

Australia

2782 posts since 5/15/2011

It will be determined by the official scale used.

In Australia it is 1:100,000. This figure then determines the MMU (minimum mapping unit) and so on.

I just did a quick search of USGS but couldn't find anything (it was a very quick search though).

Edit: found this which suggest 1:250,000 is used in the US https://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=GCMD&KeywordPath=Parameters%7COCEANS%7CCOASTAL+PROCESSES&EntryId=geodata_1088&MetadataType=0&lbnode=mdlb4

Edited by - Chris Meakin on 02/18/2020 22:40:53

Feb 19, 2020 - 3:01:15 AM
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Players Union Member

OM45GE

USA

94887 posts since 11/7/2007

It also depends on the methodology used for the measurement. There are two primary accepted methods (although there are others). The Congressional Research Service (CRS) method does not include tidal inlets and only measures ocean coastlines. The National Oceanic and Atmospheric Administration (NOAA) method includes tidal inlets and is applied to freshwater coasts as well.

The two can yield vastly different results. New Hampshire has the shortest ocean coastline buy either measure with 13 CRS miles and 131 NOAA miles. Maine has 228 CRS miles but 3,478 NOAA miles.

Alaska has the longest coastline by either method with 6,640 CRS miles and 33,904 NOAA miles.

Feb 19, 2020 - 6:37:11 AM
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Players Union Member

DC5

USA

10067 posts since 6/30/2015

Map Maker Map Maker make me a Map, Oh make me a perfect Map.

Feb 19, 2020 - 1:50:29 PM
Players Union Member

Brian T

Canada

16284 posts since 6/5/2008

Minimum Mapping Units will ignore a lot of detail which may not be of any particular value. Makes me think of Fractal Geometries.

Feb 19, 2020 - 2:55:31 PM
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mander

USA

4214 posts since 10/7/2007

quote:
Originally posted by DC5

Map Maker Map Maker make me a Map, Oh make me a perfect Map.


For Mama, make it a free app

For Papa, one that sounds like Siri

For me, well, I'd hang my cap

out for one that avoided the paparazzi!

Feb 19, 2020 - 5:31:56 PM
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nakigreengrass

New Zealand

4692 posts since 5/16/2012

My wife and I explored the coast line from Nelson to Mana ( near Wellington ) in our yacht years ago. Two cities that would be about 100 miles apart as the crow fly's, in central NZ. My log had ticked over 2,500 miles by the time we tied up to Mana marina.

Feb 19, 2020 - 5:54:19 PM

DRH

USA

305 posts since 5/29/2018

Our lake is about 25 miles top to bottom and about 10 miles left to right. But the farthest you can get away from any shoreline is about 2 miles. The official shoreline length is 525 miles. Zooming in on google earth gives the impression of a fractal.

Feb 19, 2020 - 6:05:18 PM
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2858 posts since 7/28/2015

Feb 19, 2020 - 7:59:22 PM
Players Union Member

Brian T

Canada

16284 posts since 6/5/2008

National Parks maps change from year to year. Trails are put back, trails are left off/erased. The Park wants to push people in different directions eveyr year.
Collect 40 years of maps. You'll soon see what I mean.

I worked several summers in northern Canada. We got 1:50,000 maps.
"Got your compass? What's stopping you? See you in 3 months."
You learn the level of details that the map can't or won't show you.
That lets you read the map to follow the big picture.

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