London is about 2.7 times as dense as Silicon Valley [https://www.washingtonpost.com/news/wonk/wp/2015/10/06/there-is-no-such-thing-as-a-city-that-has-run-out-o

London is about 2.7 times as dense as Silicon Valley [https://www.washingtonpost.com/news/wonk/wp/2015/10/06/there-is-no-such-thing-as-a-city-that-has-run-out-of-room/ https://www.washingtonpost.com/news/wonk/wp/2015/10/06/there...]. San Francisco has 18187/sq.mi while London has 14070 and Manhattan has 66940 [wikipedia]. Manhattan is a bit cheaper than San Francisco [http://sf.curbed.com/archives/2015/08/05/sfs_median_home_price_now_tops_manhattans_by_230k.php http://sf.curbed.com/archives/2015/08/05/sfs_median_home_pri...] so it seems population density does not explain the bay area's high prices.