How to attribute sections of a coastline to a county

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10-02-2013 05:35 AM
JulianeStruve
New Contributor
Good morning,

I have a coastline on my map (Type Line) and a shapefile of Florida counties (Type Polygon). I need to know how much of the coastline belongs to each county. Some of the lines used to describe the coastline intersect 2 or more counties.

How do I get a file that attributes every section of the coastline correctly to its county ?

What I eventually want to have is a table that attributes sections of the coastline to counties, so that I can work out how much of the coastline each county is responsible for.


Thanks a lot for any suggestions.

Juliane
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4 Replies
TimWitt
Frequent Contributor
Julian,

You could use the intersect tool, to cut your line whenever it crosses a polygon. You can then calculate the length of each feature.

After that you could do a Spatial join, with which you can bring over the length field of your lines. That should be the amount each county has to take care.
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JulianeStruve
New Contributor
Hi,

thanks a lot for replying ! I did this, but the attribute table I created contains a lot of <Null> entries that make it difficult to figure out if the results are correct. How can these be removed ?

I plotted the spatial join and the intersetion together and used as label the shape-length. I was expecting the same values for both, but while some are the same others are missing.

For example for Bird Key (Sarasota) the intersection file shows segments with lengths 840,930,740, 698, which totals to 3208. The Spatial join shows 939,698,930,740 which totals to 3407. Presumably these are meters ?

Bird Key is very small, for other area the figures do not match up at all.

How can I determine if my results are correct ? How can the lengths be aggregated by county ? That would some indication because for some counties the length of coastline is reported elsewhere or can be guesstimated.

Thanks a lot again !

Juliane
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TimWitt
Frequent Contributor
Can you share your data so I can have a look?
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JulianeStruve
New Contributor
Hi there,

I have better results now, after dissolving the County file and then intersecting with the coastline. After manually selecting the features associated with County Sarasota the summary statistics tool yields a total of app. 300 km for Sarasota, which is realistic.

I have not managed to aggregate the data by county, though. Summary statistics works on a manual selection, but gives me an error when I use it on the attribute table of my file. In the Statistics field the colum names of my attribute table appear, and I then get "The value is not a member of SUM,Mean etc."

Best,

Juliane

PS: My files are very big, so far I have not yet worked out how to attach them.
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