my plan is to create a map that shows the top 50 (by amount of passengers) international flights departing the United States (e.g. New York -> London, Honolulu -> Tokyo…). I want to use the plugin FlowMapper for QGIS to display those flights and have the width of the flows correspond with the amount of passengers. I have read the tutorial and had a look at the examples given (all in the download file of FlowMapper). The problem is, in those examples FlowMapper is only used for back and forth flows.
Thus, the data matrix in the examples looks like this, each row and column have the same:
But I want to use one way flows, so row and column have different geographical locations, like this:
So my question is, how does the flow matrix- and coordinates-file have to look like in order to be correctly displayed by the FlowMapper plugin?
This is my complete speadsheet that I wanna use as basis for my map:
http://www.sendspace.com/file/ckaejd
Best Answer
In order to work properly, FlowMapper needs a square matrix. Just reviewed your dataset and assuming that entries "New York City" and "New York" are same (since they seem to have the same coordinates) you have 38 nodes. So you would need a 38x38 matrix.
Make a list of all 38 nodes and create an empty square matrix. Then, based on your original data that you have uploaded, fill in the corresponding cells of new square matrix.
In other words, copy and paste diagonal elements on your original matrix to the proper cells on the new square matrix. Keep in mind that, if a city sends more than one flows to another city (e.g. two flights per day), just sum them, then write the total result.
Leave all other NoData cells as 0 (zero) or just assing them to e.g. 9999; so you can delete/filter later.
After all, create relevant input text files by copying values from the spreadsheet and run flow mapper. Text files, interaction matrix, node coordinates are mandatory. Node names text file is optional. Check bundled test data files for the correct format.
Good luck! (I have also send an email to you with an attachemnt)