topic Data that spans 2 grid squares in ArcGIS GeoStatistical Analyst Questions

Data that spans 2 grid squares

janehansen — Mon, 26 Oct 2015 21:07:02 GMT

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

Re: Data that spans 2 grid squares

DanPatterson_Retired — Mon, 26 Oct 2015 21:26:42 GMT

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

Re: Data that spans 2 grid squares

janehansen — Mon, 26 Oct 2015 21:30:26 GMT

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

in arc map

Re: Data that spans 2 grid squares

janehansen — Mon, 26 Oct 2015 21:47:15 GMT

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

Re: Data that spans 2 grid squares

DanPatterson_Retired — Mon, 26 Oct 2015 22:01:25 GMT

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

Re: Data that spans 2 grid squares

janehansen — Mon, 26 Oct 2015 22:11:14 GMT

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

Re: Data that spans 2 grid squares

janehansen — Thu, 29 Oct 2015 21:20:42 GMT

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

Re: Data that spans 2 grid squares

DanPatterson_Retired — Thu, 29 Oct 2015 21:30:43 GMT

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

Re: Data that spans 2 grid squares

janehansen — Thu, 29 Oct 2015 23:38:57 GMT

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.

Re: Data that spans 2 grid squares

DanPatterson_Retired — Thu, 29 Oct 2015 23:46:01 GMT

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

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 00:00:03 GMT

Thanks Dan, my file was not projected but it is now.... I added a new field and used the field calculator and the length field works just fine.

Thanks again, I think I can move forward.

Re: Data that spans 2 grid squares

DanPatterson_Retired — Fri, 30 Oct 2015 00:42:40 GMT

good news... good luck

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 19:10:54 GMT

Well, I am getting closer.

Now that I have created my split. I have two columns for length. One with the the total length of the line, and one with the split line lengths.

one set of rows for one line that spans 2 grid squares

total length field

4518

split length field

2475

2042

I am unsure how to calculate the percents using the field calculator as each set of total length and split length are unique. I can not use the query split length/total length to get the percent for each set of split lines as the query would lump all rows together

Is there a query that can be used that will separate out each set of split length rows based on the total length field and the identical values found for one set within those rows?

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 19:16:51 GMT

I have a column that is numbered 1 to... for each set of rows that correlate to a split line those numbers are duplicated...such as in the example below :

number field total length field split length field

1 4518 2475

1 4518 2042

the same applies for all the sets. Can I write a query that would identify each set based on the number field ?

Re: Data that spans 2 grid squares

DanPatterson_Retired — Fri, 30 Oct 2015 19:22:04 GMT

you shouldn't need to query, just divide the split length field by the total length field. Should you need to do a subset, ie query for 1, then perform the calculation, the field calculator does the calculations on

a selection.... just like in a spreadsheet

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 19:32:09 GMT

Ok, I thought there might be a way to do all the sub sets at once so I didn't have to select ea. subset, perform the calculation and repeat.

Thanks

Re: Data that spans 2 grid squares

DanPatterson_Retired — Fri, 30 Oct 2015 19:36:10 GMT

that is my point

if each segment has an original id number and you split it, there should be 2 or more records with the same original id, the same original length and a new length.... take the new length field and divide by the original length field.... don't be afraid...make a copy of the file first and test on the copy

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 19:39:59 GMT

I got it, thanks

Re: Data that spans 2 grid squares

DanPatterson_Retired — Fri, 30 Oct 2015 19:44:07 GMT

and everyone around you survived

Re: Data that spans 2 grid squares

janehansen — Fri, 30 Oct 2015 20:38:45 GMT

barely ha ha....thanks for sticking with me.