# What percent of earth's population live in a time zone whose UTC offset (in hours) is not a multiple of 1?

What percent of the world's population is in a timezone whose UTC offset (in hours) is not a multiple of 1?

Notes:

• To answer this, we need to know what % of the world's population live in each time zone
• A precise answer may be difficult because of changes to offsets throughout the year (e.g. with daylight savings and other adjustments)

### Example

Suppose we compare Melbourne's UTC offset to Adelaide's. Melbourne is UTC + 10 hours, whereas Adelaide is UTC + 9.5 hours.

In pseudocode / ruby:

``````time = Time.current.beginning_of_hour

time.in_time_zone("Melbourne")
# => Sun, 20 Sep 2020 15:00:00 AEST +10:00

# => Sun, 20 Sep 2020 14:30:00 ACST +09:30
``````

So we can state that (at this time of year), Melbourne's UTC offset (10) is a multiple of 1, whereas Adelaide's (9.5) is not.

### Known so far

• A cursory look at the wikipedia page on UTC offsets suggests ~11 out of 38 timezones appear to end in `30` or `45` (i.e. they don't end in `00`)
• This resource is very interesting, but doesn't appear to offer the raw data
• It suggests there are 39 time zones, however, it's from 2015, so perhaps something changed since
• This quora question offers some useful contextual graphics
• While GIS could certainly be used to solve this trivia question, there doesn't seem to be a GIS component to the question, as asked. It might be more appropriate in Puzzling (though it doesn't seem a good fit for their style). If you want to solve this yourself, you'll need to choose a GIS platform, locate current time zone and population data, then perform analysis. – Vince Sep 20 at 14:17
• @Vince this information is being used to determine the priority of a bug fix in some open source software. Right now users whose time zones aren’t multiples of 1 have degraded performance and even crashes in some cases. We need to know what % of the user base this is affecting – stevec Sep 20 at 15:15
• You can get a shapefile of timezones (github.com/evansiroky/timezone-boundary-builder/releases) and a raster of population (various sources, eg sedac.ciesin.columbia.edu/data/set/gpw-v3-population-density/… for 1 degree grid, higher resolutions available elsewhere). Aggregate raster by polygon and identify the half-hour TZs and sum. – Spacedman Sep 20 at 16:09
• It's still off-topic without an attempt, but making an Edit so that it's not worded like a Puzzling question is probably a first step in making this on-topic. – Vince Sep 20 at 16:10
• @Spacedman thank you. I managed to solve it. The answer is 21%. Workings here – stevec Sep 20 at 16:36