# Geo functions

## Geo index functions

AQL offers the following functions to filter data based on geo indexes. These functions require the collection to have at least one geo index. If no geo index can be found, calling this function will fail with an error at runtime. There is no error when explaining the query however.

### NEAR()

`NEAR(coll, latitude, longitude, limit, distanceName) → docArray`

Return at most *limit* documents from collection *coll* that are near *latitude*
and *longitude*. The result contains at most *limit* documents, returned sorted by
distance, with closest distances being returned first. If more than *limit* documents
qualify, with the distance being exactly the same among multiple documents around the
limit, it is undefined which of the qualifying documents are returned. Optionally,
the distances in meters between the specified coordinate (*latitude* and *longitude*)
and the document coordinates can be returned as well. To make use of that, the desired
attribute name for the distance result has to be specified in the *distanceName* argument.
The result documents will contain the distance value in an attribute of that name.

**coll**(collection): a collection**latitude**(number): the latitude portion of the search coordinate**longitude**(number): the longitude portion of the search coordinate**limit**(number,*optional*): cap the result to at most this number of documents. The default is 100. If more documents than*limit*are found, it is undefined which ones will be returned.**distanceName**(string,*optional*): include the distance to the search coordinate in each document in the result (in meters), using the attribute name*distanceName*- returns
**docArray**(array): an array of documents, sorted by distance (shortest distance first)

### WITHIN()

`WITHIN(coll, latitude, longitude, radius, distanceName) → docArray`

Return all documents from collection *coll* that are within a radius of *radius*
around the specified coordinate (*latitude* and *longitude*). The documents returned
are sorted by distance to the search coordinate, with the closest distances being
returned first. Optionally, the distance in meters between the search coordinate and
the document coordinates can be returned as well. To make use of that, an attribute
name for the distance result has to be specified in the *distanceName* argument.
The result documents will contain the distance value in an attribute of that name.

**coll**(collection): a collection**latitude**(number): the latitude portion of the search coordinate**longitude**(number): the longitude portion of the search coordinate**radius**(number): radius in meters**distanceName**(string,*optional*): include the distance to the search coordinate in each document in the result (in meters), using the attribute name*distanceName*- returns
**docArray**(array): an array of documents, sorted by distance (shortest distance first)

### WITHIN_RECTANGLE()

`WITHIN_RECTANGLE(coll, latitude1, longitude1, latitude2, longitude2) → docArray`

Return all documents from collection *coll* that are positioned inside the bounding
rectangle with the points (*latitude1*, *longitude1*) and (*latitude2*, *longitude2*).
There is no guaranteed order in which the documents are returned.

**coll**(collection): a collection**latitude1**(number): the bottom-left latitude portion of the search coordinate**longitude1**(number): the bottom-left longitude portion of the search coordinate**latitude2**(number): the top-right latitude portion of the search coordinate**longitude2**(number): the top-right longitude portion of the search coordinate- returns
**docArray**(array): an array of documents, in random order

## Geo utility functions

The following helper functions do **not use any geo index**. On large datasets,
it is advisable to use them in combination with index-accelerated geo functions
to limit the number of calls to these non-accelerated functions because of their
computational costs.

### DISTANCE()

`DISTANCE(latitude1, longitude1, latitude2, longitude2) → distance`

Calculate the distance between two arbitrary coordinates in meters (as birds would fly). The value is computed using the haversine formula, which is based on a spherical Earth model. It's fast to compute and is accurate to around 0.3%, which is sufficient for most use cases such as location-aware services.

**latitude1**(number): the latitude portion of the first coordinate**longitude1**(number): the longitude portion of the first coordinate**latitude2**(number): the latitude portion of the second coordinate**longitude2**(number): the longitude portion of the second coordinate- returns
**distance**(number): the distance between both coordinates in meters

```
// Distance between Brandenburg Gate (Berlin) and ArangoDB headquarters (Cologne)
DISTANCE(52.5163, 13.3777, 50.9322, 6.94) // 476918.89688380965 (~477km)
// Sort a small number of documents based on distance to Central Park (New York)
FOR doc IN documentSubset // e.g. documents returned by a traversal
SORT DISTANCE(doc.latitude, doc.longitude, 40.78, -73.97)
RETURN doc
```

### IS_IN_POLYGON()

Determine whether a coordinate is inside a polygon.

`IS_IN_POLYGON(polygon, latitude, longitude) → bool`

**polygon**(array): an array of arrays with 2 elements each, representing the points of the polygon in the format*[lat, lon]***latitude**(number): the latitude portion of the search coordinate**longitude**(number): the longitude portion of the search coordinate- returns
**bool**(bool):*true*if the point (*latitude*,*longitude*) is inside the*polygon*or*false*if it's not. The result is undefined (can be*true*or*false*) if the specified point is exactly on a boundary of the polygon.

```
// will check if the point (lat 4, lon 7) is contained inside the polygon
IS_IN_POLYGON( [ [ 0, 0 ], [ 0, 10 ], [ 10, 10 ], [ 10, 0 ] ], 4, 7 )
```

`IS_IN_POLYGON(polygon, coord, useLonLat) → bool`

The 2nd parameter can alternatively be specified as an array with two values.

By default, each array element in *polygon* is expected to be in the format *[lat, lon]*.
This can be changed by setting the 3rd parameter to *true* to interpret the points as
*[lon, lat]*. *coord* will then also be interpreted in the same way.

**polygon**(array): an array of arrays with 2 elements each, representing the points of the polygon**coord**(array): the search coordinate as a number array with two elements**useLonLat**(bool,*optional*): if set to*true*, the coordinates in*polygon*and the search coordinate*coord*will be interpreted as*[lon, lat]*. The default is*false*and the format*[lat, lon]*is expected.- returns
**bool**(bool):*true*if the point*coord*is inside the*polygon*or*false*if it's not. The result is undefined (can be*true*or*false*) if the specified point is exactly on a boundary of the polygon.

```
// will check if the point (lat 4, lon 7) is contained inside the polygon
IS_IN_POLYGON( [ [ 0, 0 ], [ 0, 10 ], [ 10, 10 ], [ 10, 0 ] ], [ 4, 7 ] )
// will check if the point (lat 4, lon 7) is contained inside the polygon
IS_IN_POLYGON( [ [ 0, 0 ], [ 10, 0 ], [ 10, 10 ], [ 0, 10 ] ], [ 7, 4 ], true )
```