# Measurement Objects¶

The `django.contrib.gis.measure` module contains objects that allow for convenient representation of distance and area units of measure.  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_benoit`

`link_sears`

`clarke_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