A better starting image (although it is rotated 180 degrees) is in the section “The Shape of the Milky Way - The Evidence” here:
This appears to have been copied directly from one of the maps in a series of important scientific papers on Milky Way structure from Hiroyuki Nakanishi and Yoshiaki Sofue. Eg:
Actually, even better to use the image in that paper. I suspect that the Wikipedia image is a dumbed down version of that.
A while back, I overlaid my data on top of the Nakanishi and Sofue molecular hydrogen map and found a reasonably close match.
The good thing about the Hiroyuki Nakanishi and Yoshiaki Sofue map is that it reveals how “flocculent” different parts of the Milky Way are. Flocculence is a measure of how much a galaxy departs from the grand design spiral arm scheme. For example, the Perseus arm seems quite flocculent, and the Sagittarius/Carina arm less so.
Here’s an example of a highly flocculent galaxy:
Keep in mind that the idea that the Milky Way has four distinct spiral arms is actually far more speculative than many people realise. It is not that easy to see these arms in the Hiroyuki Nakanishi and Yoshiaki Sofue map although they do their best to find them in the article I linked to above.
I have re-uploaded star_data.xls and you should be able to get it now from my Sources page. Thanks for pointing out the problem.