River network distance to source for fish

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Heiko

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Jan 12, 2018, 7:31:53 AM1/12/18
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Hey guys,
I need to model fish occurences in a river network.

One important predictor would be the "distance to source" (meaning the distance of a population/individual to the source of the river segment).
I got this calculated for every occurrence point. But now I dont know how to proceed. I would also need it for a random number of background points right? Or even as a constant raster in my whole river network?

Any advice on how to move forward with this predictor in ArcGis would be very very welcome.
Thank you!!!

Heiko

Jacek Stefaniak

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Jan 12, 2018, 7:45:27 AM1/12/18
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Hi,


I got this calculated for every occurrence point.
 

I'll come to this from different perspective - you need map of whole terrain/river network with this distances, not only for your occurrence points - because for MaxEnt you should have random points too. You should construct raster map with distances for every raster pixel in standard (linear) way (like this) or, if you want use real river course, use "road cost distance" map (like this). Unfortunately, I do not know, how do it in Arc, but freeware SAGA GiS program has such options.

Hope that helps,

J.

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Heiko

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Jan 12, 2018, 8:47:22 AM1/12/18
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Thank you for your input Jacek. I am afraid you are right. Does anyone know how I can create a raster map with the distance to source for every raster pixel? It would have to be the real river course though, not the linear way!!

I would be grateful for any idea how to solve this.
Thank you!
Heiko

Jacek Stefaniak

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Jan 12, 2018, 9:26:50 AM1/12/18
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Hi,

https://desktop.arcgis.com/en/arcmap/10.3/analyze/commonly-used-tools/proximity-analysis.htm - I hope that help, but if you work on raster, you should treat each river separately (if you have more than one river) because if River_1 source is close to River_2 source it can distort your results. You can use vector file, too - you just must generate points/lines representing distances from source (from each river separately) and rasterize it by estimating or kriging.

Or you can use https://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/cost-distance.htm this tool for arc, and set  in input cost raster land as No Data - it should do the trick.

But I want point two things:

1) Cost distance is accumulated - it means that your fish travel from source to point of occurrence. In your case, I dont know that is a true or not - so maybe you should use standard distance instead of cost map.
2) If you want work on raster maps, you should have a raster map of river network - because in shp (vector) file rivers very often are treated as lines, mean they do not have width. If you plan convert shp to raster, you should transform lines to polygons, with accurate width of each river (and be sure that all your occurrence points are "in" that polygon too).

I hope that I make sense and write clearly. I work with fishes too, so if you have more questions, ask* ;)

*but I am not a very advanced gis-user, so handle my opinions with necessary caution

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Heiko

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Jan 12, 2018, 10:02:44 AM1/12/18
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Thank you very much! I will look into it ASAP.
If anyone with advanced GIS skills has more information, I would appreciate your input or ideas.

Have a nice weekend,
Heiko
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