I once read that Maps and Gmail (not sure why they were combined) have a software maintenance cost of over $40M per month.
That includes payroll for real Employees of the Goog, marketing costs, spending accounts for marketing etc.
Thats why programs like LocalGuide, Trusted and such are genius. Google keeps their overhead costs down by getting their users to provide them with human curation of Maps data, and they do it for some badges and 100G of drive space (BTW thanks for that Googalicious)
Google human engineering is just as awesome as Google software and web services engineering.
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Imthemobile.guru