# calculate coastline at risk

I have an idea of what I want to do but I don't know yet what tools will bring me there.

I have administrative boundaries in one layer and coastline in another layer. The coastline is categorized in different classes. What I want to find out is how much of each category falls into each administrative boundary. So the outcome would be percentages of the administrative unit's coastline for each class. So say the coastline from unit 1 is 40% class A, 50% class B and 10% class C. Unfortunately, the two shapefiles do not match up exactly because one of them does not have a spatial reference...? (I work with ArcMAP10)

Any hints and ideas what tool will bring me there? Any help is greatly appreciated Sandra

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Coastline is a polyline, and boundaries are polygons or also polylines? Can you post a picture of your data? If it is a big area, just a part of it, to see the classes along an administrative unit – nadya Oct 16 '12 at 0:35
The coastline consists of many small lines of different length (not even continous), they all carry attributes like the type of coast, length and what risk category they are. The administrative boundaries are polygons. – Sandra Oct 17 '12 at 15:55

I would suggest you to do a thin buffer for the boundaries or the coastline, until one layer completely covers another. Then you can use Split tool to split the coastline according to administrative areas, and then Spatial join tool to attach to the administrative areas the corresponding pieces of the coastline. And firstly to better match the layer you can use Spatial adjustments.

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Thank you so much for your help. I did create a buffer around the administrative boundaries and then used spatial join (with the setting set to the buffer layer conatins the coastline layer) to add the attributes from the coastline layer to the administrative boundaries layer. I skipped the Split tool. I have a slight idea what that could mean for my results. Does that mean I might have used coastline pieces that span over two administrative boundaries twice?..or that there is somekind of issue with that? – Sandra Oct 15 '12 at 21:32
Yes, I think you can have in one administrative unit coastline pieces which continue to another unit. So you cannot calculate percentages correctly, because they depend on length, right? – nadya Oct 15 '12 at 23:44
I would say firstly you split coastline by administrative units, then add a field in the attribute table and calculate length there, then join (one-to-many). The attributes from the coastline piece of each class should go to the target administrative units (the administrative units will multiple in the output table according to the number of the coast classes). Then calculate for each administrative unit for each coastline class = length of the class / total coast length in this unit – nadya Oct 15 '12 at 23:44
Hi Nadja, I would love to do that, but if I try to split the coastline by administrative unit, there is no output? It says the tool is done but nothing happens? – Sandra Oct 16 '12 at 0:29

If the two datasets are showing up in the same area in ArcMap it's likely they have projections defined, allowing ArcMap to reproject on the fly. Because they're not exactly over the top of each other its likely that the original sources are different, which can potentially make things a bit more difficult.

I'm assuming that the classifications don't line up against the administrative boundary, so the first step would be to split the coast line up. You could do this manually in an editing session in ArcMap, but I think the easiest way to do this would be to use the Feature Vertices to Point tool on your administrative boundaries and then the Split Line at Point tool (with a search radius) to split up the data.

Once you've got the data split up then the easiest way to go would be to use Spatial Join on the split coastline and join on the closest administrative boundary (so your coastline sections get an extra attribute of boundary name for instance) - again you'd likely need a search radius.

At this point make sure you have a length field calculated for each coastal section, and then lastly you can use Summerize to aggregate the data together and get your results (alternately export to Excel and use a Pivot Table to aggregate the data).

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Thanks so much for your answer, I think I get your point now. As I noticed that the spatial join runs into troubles if I don't split the coastline, as it will only include the ones that are completely within. The coastlines that spans over two administrative units get lost. The problem is though that the coastline is too complex and if I apply the Feature Vertices to points I get way too many points. Isn't there a tool that would use the admin. boundaries to cut the lines? Or is this wishful thinking? – Sandra Oct 15 '12 at 23:06
The Cut Features tool should do what you want. If not take a look at Methods for Splitting Line Features. – om_henners Oct 16 '12 at 5:38
Thanks for mentioning that, I was looking at the cut features tool and that looks very promising. Unfortunately, although I do have the ArcInfo license, the start editing field stays greyed out...Any idea? The shapefile is editable so it's not locked..it might be some kind of other license issue as I am accessing ArcMap through an online server..any ideas? – Sandra Oct 17 '12 at 23:32