Question about several Google Maps query string fields

Question

Given the following Google Maps query string, http://maps.google.com/maps?f=q&source=s_q&tab=ll&hnear=washington+dc&q=1600%20pennsylvania%20avenue,
What do the following fields mean?

1. source (and what does the value s_q mean)
2. hnear
3. tab

Additionally, what are possible values for these fields?

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Also, a decent reference for most other query string fields can be found here http://querystring.org/google-maps-query-string-parameters/

Answer 1

1. hnear is the location which should be used as a reference location and searched nearby. So if it has washington as value, it'll search for places near Washington.

2. source and tab are not only for Google Maps. They are just two of few flags Google uses in their variety of products to track the usage of the user. Hence, of course, Google doesn't document them. You can read more about them in this fantastic blog post.

P.S. Google keeps changing these parameters, so few of them might seem obsolete.