IACs are short, tryte-encoded, location codes that can be used to tag and retrieve IOTA transactions related to specific locations. The IACs are typically 11 trytes long and will represent a 13.5m by 13.5m area, at the equator. However IACs can be 12 trytes long and represent a 2.8m by 3.5m grid.
For example: In IAC, you can represent the location of the IOTA Foundation's registered address as
NPHTQORL9XK
IACs are a direct copy of the Open Location Codes, also known as Plus Codes, proposed by Google Zurich in 2014. There are a few minor changes to make it compatible with IOTA's encoding. Compare the differences below which are as follows:
| OLC | IAC | |
|---|---|---|
| Example | 9F4MGCH7+R6F |
NPHTQORL9XK |
| Alphabet | 23456789CFGHJMPQRVWX |
FGHJKLMNOPQRSTUVXWYZ |
| Separator | + |
9 |
| Padding | 0 |
A |
Plus codes are based on latitude and longitude – the grid that can be used to describe every point on the planet. By using a simpler code system, they end up much shorter and easier to use than traditional global coordinates.
A plus code in its full length is 10 characters long, with a plus sign before the last two. It consists of two parts:
- The first four characters are the area code, describing a region of roughly 100 x 100 kilometers.
- The last six characters are the local code, describing the neighborhood and the building, an area of roughly 14 x 14 meters – about the size of one half of a basketball court.
Each code uses these two parts to locate a larger region and then find the precise location within that region.
For those needing more precision, an additional, optional character can be used to improve accuracy to roughly 3 x 3 meters – about the size of a small car. The code length excludes the separator.
| Code length | 2 | 4 | 6 | 8 | + | 10 | 11 |
|---|---|---|---|---|---|---|---|
| Block size | 20° | 1° | 0.05° (3′) | 0.0025° (9″) | 0.000125° (0.45″) | ||
| Approximately | 2200 km | 110 km | 5.5 km | 275 m | 14 m | 3.5 m |
When publishing information on IOTA there is no way to easily identify transactions that relate to a geographic areas. These transactions could contain localised service advertisements, sensor information or any number of other data formats.
In order to find transactions related to an area you'd have to register your transactions with a centralised service, like a data marketplace, that collects locations to store and serve it to consumers. By using IACs in the first 12 trytes of the 27 tryte tag field in an IOTA transaction, we can localise an IOTA transaction to a 2.8m by 3.5m area. This allows for someone to find a transaction related to a small area, however the real value of this system comes from the ability to query large swaths of land for related transactions.
The original OLC protocol is able to accurately represent areas on the globe by using 5 pairs of characters. Each pair of characters added to the code represent a 400x increase in accuracy. A side effect of the code being determined by a set of pairs, rather than a unique code, is we are able to vary the accuracy by removing pairs from right to left. This allows us to ingest and store the pairs in a way that we can query some what efficiently.
So by querying the initial 4 trytes of tags, that match the correct IAC format, we can find transactions in a 100km by 100km area. By querying for all tags that start with NPHT we can find all items in a 100km by 100km area covering Berlin & parts of Potsdam. Then by using these 6 trytes: NPHTQO we are able to see transactions within a few suburbs in central/north Berlin.