# Measurement Objects¶

The `django.contrib.gis.measure` module contains objects that allow for convenient representation of distance and area units of measure. [1] Specifically, it implements two objects, `Distance` and `Area` – both of which may be accessed via the `D` and `A` convenience aliases, respectively.

## Example¶

`Distance` objects may be instantiated using a keyword argument indicating the context of the units. In the example below, two different distance objects are instantiated in units of kilometers (`km`) and miles (`mi`):

```>>> from django.contrib.gis.measure import D, Distance
>>> d1 = Distance(km=5)
>>> print(d1)
5.0 km
>>> d2 = D(mi=5) # `D` is an alias for `Distance`
>>> print(d2)
5.0 mi
```

For conversions, access the preferred unit attribute to get a converted distance quantity:

```>>> print(d1.mi) # Converting 5 kilometers to miles
3.10685596119
>>> print(d2.km) # Converting 5 miles to kilometers
8.04672
```

Moreover, arithmetic operations may be performed between the distance objects:

```>>> print(d1 + d2) # Adding 5 miles to 5 kilometers
13.04672 km
>>> print(d2 - d1) # Subtracting 5 kilometers from 5 miles
1.89314403881 mi
```

Two `Distance` objects multiplied together will yield an `Area` object, which uses squared units of measure:

```>>> a = d1 * d2 # Returns an Area object.
>>> print(a)
40.2336 sq_km
```

To determine what the attribute abbreviation of a unit is, the `unit_attname` class method may be used:

```>>> print(Distance.unit_attname('US Survey Foot'))
survey_ft
>>> print(Distance.unit_attname('centimeter'))
cm
```

## Supported units¶

Unit Attribute Full name or alias(es)
`km` Kilometre, Kilometer
`mi` Mile
`m` Meter, Metre
`yd` Yard
`ft` Foot, Foot (International)
`survey_ft` U.S. Foot, US survey foot
`inch` Inches
`cm` Centimeter
`mm` Millimetre, Millimeter
`um` Micrometer, Micrometre
`british_ft` British foot (Sears 1922)
`british_yd` British yard (Sears 1922)
`british_chain_sears` British chain (Sears 1922)
`indian_yd` Indian yard, Yard (Indian)
`sears_yd` Yard (Sears)
`clarke_ft` Clarke’s Foot
`chain` Chain
`chain_benoit` Chain (Benoit)
`chain_sears` Chain (Sears)
`british_chain_benoit` British chain (Benoit 1895 B)
`british_chain_sears_truncated` British chain (Sears 1922 truncated)
`gold_coast_ft` Gold Coast foot
`link` Link
`link_benoit` Link (Benoit)
`link_sears` Link (Sears)
`clarke_link` Clarke’s link
`fathom` Fathom
`rod` Rod
`furlong` Furlong, Furrow Long
`nm` Nautical Mile
`nm_uk` Nautical Mile (UK)
`german_m` German legal metre

Note

`Area` attributes are the same as `Distance` attributes, except they are prefixed with `sq_` (area units are square in nature). For example, `Area(sq_m=2)` creates an `Area` object representing two square meters.

## Measurement API¶

### `Distance`¶

class `Distance`(**kwargs)[source]

To initialize a distance object, pass in a keyword corresponding to the desired unit attribute name set with desired value. For example, the following creates a distance object representing 5 miles:

```>>> dist = Distance(mi=5)
```
`__getattr__`(unit_att)

Returns the distance value in units corresponding to the given unit attribute. For example:

```>>> print(dist.km)
8.04672
```
classmethod `unit_attname`(unit_name)

Returns the distance unit attribute name for the given full unit name. For example:

```>>> Distance.unit_attname('Mile')
'mi'
```
class `D`

Alias for `Distance` class.

### `Area`¶

class `Area`(**kwargs)[source]

To initialize an area object, pass in a keyword corresponding to the desired unit attribute name set with desired value. For example, the following creates an area object representing 5 square miles:

```>>> a = Area(sq_mi=5)
```
`__getattr__`(unit_att)

Returns the area value in units corresponding to the given unit attribute. For example:

```>>> print(a.sq_km)
12.949940551680001
```
classmethod `unit_attname`(unit_name)

Returns the area unit attribute name for the given full unit name. For example:

```>>> Area.unit_attname('Kilometer')
'sq_km'
```
class `A`

Alias for `Area` class.

Footnotes

 [1] Robert Coup is the initial author of the measure objects, and was inspired by Brian Beck’s work in geopy and Geoff Biggs’ PhD work on dimensioned units for robotics.