OPEN LOCATION CODE FREQUENTLY ASKED QUESTIONS

Q: What is Open Location Code for?
A: Open Location Code provides short codes that people can use to refer to
locations, when street addresses don't exist, aren't known or aren't suitable.

Q: What are the specific aims?
A: The aims are to have codes that are shorter and easier to use than
latitude and longitude coordinates. The codes should be short enough that
people can remember them and communicate them in speech or in writing. The
codes should work offline, should not include words and should not require
setting up. It should be possible to tell if two codes are close to each
other by looking at them.

Q: Where do we expect Open Location Code to be useful?
A: More than half the world's urban dwellers live on streets that don't have
formal names. We expect these codes will be mostly used by people in areas
lacking street addresses, but could also be used in areas that are mapped
but where street name data is not widely available or where both formal and
informal names exist.

Q: Should cities stop naming streets?
A: No! Street naming provides numerous benefits, including cementing a sense
of identity for residents and connecting them to their community. Based on
the World Banks experience, though, street naming projects typically take in
the order of one to two years (depending on the size of the city), and cost
approximately $5USD per addressed building. The advantage of Open Location
Codes is that they are available now to anyone with access to a computer or
smartphone.

Q: Are there uses for Open Location Code in well-mapped countries?
A: Yes, for example Switzerland has villages where multiple streets have the
same name. The UK has some homes that are identified by names, rather than
by street numbers. Venice and Japan both have block-based addresses, rather
than street name based. In addition, there are locations where people wish
to meet but the best street address is not useful - for example, a picnic
spot within a park, a mountain hut or a ski lift.

Q: How does Open Location Code differ from latitude and longitude?
A: Latitude and longitude are two signed numbers. They have different
ranges, and the order matters. For five decimal places, roughly 10 meter
accuracy, latitude and longitude require between 15 and 20 text characters
("0.39122, 9.45225" to "-43.95134,-176.55053"). Latitude and longitude
express a point location, and there is no universally accepted way to
provide a location of something that is not a point, such as a football
field, park or lake.

The problem of poor or no addresses has existed for ever, and cheap GPS
devices for at least 15 years, and yet latitude and longitude coordinates
are still not widely used by people to specify destinations. We think that
this shows latitude and longitude are just too complicated for normal use.

Q: How do short codes differ from full codes?
A: A full code encodes a globally unique location and can be decoded offline
and without any additional data. Short codes are generated from full codes
by dropping characters from the start, which means that they can only be
decoded relative to a reference location. This reference location must be
communicated with the short code, if it isn't shared knowledge of all parties
involved.

Q: How can a reference location be communicated with a short code?
A: Often, a reference location can be assumed to be shared knowledge and
does not need to be explicitly given. For example, when talking to someone
in the same city and agreeing to meet them at "G98H+F2", there will typically
be just one location with that short code in any given city.

If a reference location needs to be communicated, it is often sensible to
just append the name of the city. For example, if postal or rescue services
in an area make use of Open Location Code, using "G98H+F2 Berlin" should allow
mail to be delivered or an ambulance to navigate to its intended destination.
If short codes need to be encoded and decoded algorithmically, for example by
using a lookup table or by making use of a (reverse) geocoding API, the same
data or API should be used for both encoding and decoding.

Q: Can a global lookup table for short codes be added to this repository?
Providing this data is not within the scope of this repository, and issues
opened to request such data will be closed. If online geocoding APIs can not
be used, it is often useful to first think about the actual requirements of
the Open Location Code application, as regional instead of global data will
often suffice. This data might already exist for a specific application, or
can potentially be extracted from open GIS or map data available online.
The community mailing list can be used to ask for help with such data.

Q: Why doesn't Open Location Code include altitude?
A: We didn't want to append it as a suffix or bury it in the code because we
want to be able to truncate the codes reliably. We also didn't want to
unnecessarily extend the length of codes for what we expect to be a minority
of cases. Altitude is more useful to people as a floor number, but there are
different ways of numbering building floors depending on local custom.

In summary, we couldn't think of a way that was better than specifying the
code and allowing people to just say "3rd floor".

Q: Why does Open Location Code use two algorithms?
A: The first algorithm provides codes that can be visually compared and
sorted. This is used until the code is 10 characters long, with a resolution
of 1/8000th of a degree, approximately 14 meters. This will often be
sufficient, but in some cases of high density buildings this will be too
large. Continuing with this algorithm adds two more characters for a
resolution of 70 centimeters.

We want to keep the length of the codes low to make them easier to remember
and use. We didn't feel that the resolution was necessary, and so the second
algorithm is used to refine the code with just a single character, with a
resolution of 1/40000 x 1/32000 of a degree (approximately 3.5 x 2.8 meters).

If we had based the entire code on the second algorithm, we would have codes
that would not be reliably visually comparable or sortable by proximity.

Q: Why is Open Location Code based on latin characters?
A: We are aware that many of the countries where Plus Codes will be
most useful use non-Latin character sets, such as Arabic, Chinese, Cyrillic,
Thai, Vietnamese, etc. We selected Latin characters as the most common
second-choice character set in these locations.

We considered defining alternative Open Location Code alphabets in each
character set, but this would result in codes that would be unusable to
visitors to that region.

Q: Why doesn't Open Location Code include a checksum?
A: One of the aims is to make the codes short to enable their everyday use,
in writing and speech. We felt that adding checksums when codes are being
communicated between computers is unnecessary, and adding checksums when
codes are being communicated between people reduces the usability and will
mostly be worked around ("We're meeting in Miami in an hour? But we're in
Hyderabad!") because users will realise that a code cannot possibly be
correct. It's analogous to someone using the wrong suburb name today - it
happens, people are able to deal with it.

Q: Why do Plus Codes look like something fell on my keyboard?
A: We wanted something that wasn't linked to a single culture, so word-based
codes were out. That meant that the codes would be essentially a number, but
we used letters as well as digits to raise the number base and shorten the
codes, to make them easier to remember. After we eliminated some letters and
digits to avoid spelling words and to remove easily confused pairs, we got
the current set of symbols. One disadvantage of the symbol set is that it is
noncontiguous, although it is difficult to see how we could change that
without violating any of the aims.

Q: What coordinate system does Open Location Code use?
A: Open Location Code should be based on WGS84, since this is the datum
used by GPS and is how coordinates on smartphone devices are made available.
There is nothing to prevent coordinates using other datums being used, but
when decoded by someone who expects them to be WGS84, it may result in a
different location.

Q: Why do Open Location Code areas distort at high latitudes?
A: Plus Codes are a function of latitude and longitude. As
longitude lines converge on the north and south poles the areas become
narrower and narrower. At the equator codes are square, but at about 60
degrees latitude, the codes are only half as wide.

Q: Are there any discontinuities in the codes?
A: Yes, codes on either side of the 180 longitude line will be very
different, even though they may be very close together. Apart from some
islands in the Fiji group, there are almost no affected inhabited areas, and
we feel this is acceptable. The other discontinuities are at the poles, but
as these do not have large permanent populations we don't expect significant
use of Open Location Code here.

Q: What about continental drift?
A: Most tectonic plates are moving at rates of 1-5cm per year. With the 10
character Plus Code representing 14x14 meter boxes, codes should be valid for
many years. Even the more accurate 11 character codes should not require
updating for 30-50 years. But even if they do, the worst result is that
someone using a code will find themselves at the home or building
next door.
