Perhaps, I do not fully understand completely, but would it not be simpler to just rearrange the key (and partition) by date & location?
EG: 2015_01_01_metrics_location_XXXXX
In that way, you would only have 365 partitions per year at most. But you also have the option to break it down by week or month, or year.
EG:
EXTRACT(YEAR FROM utc_time) = 2015 AND
EXTRACT(WEEK FROM utc_time) = 1
or
EXTRACT(YEAR FROM utc_time) = 2015 AND
EXTRACT(MONTH FROM utc_time) = 1
or just
EXTRACT(YEAR FROM utc_time) = 2015