Hacker News Reader

Comment by ryandrake | Hacker News Reader

Don’t forget that time zone boundaries often change, so if you are going to store a “time zone” field, make sure you regularly update them.

You are right about the lack of availability of complete airport data. This is true for many things aviation related, including airspace boundaries, navigation aids, etc. Basically anything you would find on a pilot’s chart. The USA is a wonderful exception as they publish a great deal of info digitally and for free, but this is not true for most other countries. Many countries cartographic offices (or their private contractors) even claim copyright over basic facts like “airport ABC is at location X” and “navaid DEF transmits on frequency 123”. It’s crazy that information that potentially could save lives are locked up behind rent extracting corporations and intellectual property laws.

View on HN

Yeah, the US and Canada are fantastic exceptions to the normal rule of making aeronautical information impossible to find and use. It really sucks that GA is so much more rare outside of North America. For all the bitching we do about the FAA, they're a generally pretty good organization that actually wants people to fly. The vibe I get from most other countries' aviation authority is that they just don't want us up there and that we're a pest or threat. They make it expensive and regulate it into the ground, or worse, ban GA altogether. In the US, airspace is, for the most part, open or easy to get clearance to (barring the presidential TFR and DC ADIZ nonsense), getting a license is more or less easily attainable, and buying or renting an aircraft is super easy. This isn't really the case anywhere else in the world.

> Don’t forget that time zone boundaries often change

I always thought time zones boundaries were static... TIL

Actual time zone boundaries have on average 2-3 changes a year. Sudan recently hopped back an hour for example, a separatist state in eastern Ukraine switched to Moscow time and Russia changed the time zones of a bunch of cities last year.

What does happen more often is people screwing around with Daylight savings. Each year probably a dozen countries decide to change how they're going to do daylight savings, either by canceling or reintroducing it or moving the date when the changeover happens. And the you get some real oddities like Morocco (I think it was) a few years ago the decided to temporarily suspend daylights saving during Ramadan (what do you mean your software cannot handle having an arbitrary number of dates for the start and end of daylight saving each year)

World "timezone" boundaries, in terms of which regions of the world adhere to what offset, sometimes move around. This is what most people think of when talking about timezones, in that they're talking about regions of the world in aggregate by offset: e.g. every place that's UTC+03:00. Seasonal shifts like Daylight Saving complicate this blanket definition further.

The IANA Timezone Database flips the definition to be local instead of global, and attempts to define a timezone as a region in which all clocks are supposed to have agreed since the 1970 Unix Epoch [1]. Furthermore, since governments are the most frequent source of official timekeeping changes, they attempt to prevent zones from crossing international boundaries.

Typically, IANA timezones (whose geographical extent is documented in shapefiles) don't change shape, or change shape only with national borders themselves. When a country decides to change clocks only in a portion of its territory -- "splitting" an existing IANA zone -- a new zone is created for the area that does not include the city after which the zone is named. Some recent examples are the island of Cyprus [2] and a new timezone surrounding Tomsk [3] in Russia.

[1] https://data.iana.org/time-zones/theory.html [2] https://mm.icann.org/pipermail/tz/2016-October/024399.html [3] https://mm.icann.org/pipermail/tz-announce/2016-April/000038...

Reply on news.ycombinator.com