Data that spans 2 grid squares

[janehansen]

I have a polygon grid that covers the an area of concern, I have created polylines from the fishing events, each fishing event is associated with the number of salmon caught.  Some of the lines span two grid squares.  I need to rank the grids based on the number of salmon caught.  If the line spans two grids what grid should be ranked highest is one question.  We don't know if the majority of the fish were caught in one grid square or the other so how can you defend that one or the other grid square should be ranked the highest. 

Is there a way to address this is the most defensible way possible?

Thanks

[DanPatterson_Retired · Accepted solution]

finicky question, a couple of options. the first would be to intersect the lines with each grid square after calculating the line lengths.  Those that get split and are not fully contained, you could calculate a new length field then aportion the catch to each side of the line, this of course assumes the catch is uniform along the line.  Another option is to use a select by location for each grid using the completely within option.  You then summarize the data for those samples for each grid square.  Then perform a query for those not completely within either grid square and summarize those as a third population.  The options could go on, but this will give you something to think about

[janehansen]

Thanks Dan, I'll think about these options while reviewing the data again

in arc map

[janehansen]

Hi Dan, I plan to calculate the percent that each line is found in each grid square, then take the value of the line and distribute it based on the percent of the line in a square.

Example:

line value= 30

line is found in 3 squares

10%

30%

70%

I want to show correct percent of 30 in each square.

Do you know of a tool that can calculate the percent of a polyline contained within a grid square.

I believe once I find that I can create a new field and use the field calculator to calculate the squares value.

Any thoughts you might have as to the best way to do this would be great.

Thanks,

Jane

[janehansen]

Hey Dan, if I have a field in excel and need to remove the first for

letters from that field...e.g. stfb 19 and I want to remove the stfb what

would the formula be? I tried =right (A2,len(A2-find("",AD)) but that

didnt work.

I am just learning this so I thank you very much for the time you have

spent helping me.

Jane

[DanPatterson_Retired]

use excel rarely but assuming A1 contains ABCD1234 how about =RIGHT(A1,LEN(A1)-4) of course if the cells aren't the same and/or any spaces after the first four you will have to adjust.  Then copy down the column if arranged columni-wise

[janehansen]

Thanks Dan, that worked but you are right the cells are not the same some

have different number after the letters. I'll work with what you have

given me and see if I can figure it out.

Jane

[DanPatterson_Retired]

as suggested, if you intersect the lines with the grid polygons:

Intersect—Help | ArcGIS for Desktop

using the Polygon and Line input with line output as shown here How Intersect works—Help | ArcGIS for Desktop

you can then can calculate the line length as per usual or if in a geodatabase, they will be calculated for you

[janehansen]

Thanks Dan, so that worked beautifully.  The only problem is that I needed the length to be in nautical miles so I tried to add a field and populate it using the calculate geometry.  I am unable to complete the calculation, it tells me that the length is disabled. 

I am using a gbd that does give me the length, but I don't know what units it is using.

thanks for all your help.

[DanPatterson_Retired]

Just add a new field (Length2, double) and set that field to the Shape_Length field (or whatever it is called in a geodatabase).  I am praying that you have a file that has a projected coordinate system and that its units are projected.  in otherwords, are you lengths tiny or do they look like meters or feet?  If the latter (or former)), check the properties of the layer and determine the coordinate system and its units.  You will be able to update the new Length2 field by multiplying it back the factor needed to convert it from ??? to nautical miles