Which has more entries, BDB or Strong's Hebrew?
Is there any known mapping between the two?
OK, I'm going to answer it myself, based on the comments above.
1 Strongs entry -> possibly multiple BDB entries
Apparently, because Hebrew words can be browsed by Strong's entry at concordances.org/hebrew, and each entry is linked to a BDB entry, then there is at most 1 BDB entry per Strong's entry, and the two are mapped (from Strongs to BDB) at that URL.
Strongs > BDB
Shemmy's reasoning seems good. Strong's is exhaustive. I believe BDB is also exhaustive, but it is organized by one entry per tri-radical root. Being that Strong's contains multiple entries per root, and BDB contains only one entry (containing multiple instances of that root in the text), Strong's is bound to have more entries.