# Getting startedΒΆ

The cleanest way to use the functionality in healpix is to make use of the high-level `HEALPix` class. The `HEALPix` class should be initialized with the `nside` parameter which controls the resolution of the pixellization - it is the number of pixels on the side of each of the 12 top-level HEALPix pixels:

```>>> from astropy_healpix import HEALPix
>>> hp = HEALPix(nside=16)
```

As described in the references above, HEALPix pixel indices can follow two different ordering conventions - the nested convention and the ring convention. By default, the `HEALPix` class assumes the ring ordering convention, but it is possible to explicitly specify the convention to use using the `order` argument, for example:

```>>> hp = HEALPix(nside=16, order='ring')
```

or:

```>>> hp = HEALPix(nside=16, order='nested')
```

Once this class has been set up, you can access various properties and methods related to the HEALPix pixellization. For example, you can calculate the number of pixels as well as the pixel area or resolution:

```>>> hp.npix
3072
>>> hp.pixel_area
<Quantity 0.0040906154343617095 sr>
>>> hp.pixel_resolution
<Quantity 219.87113035631398 arcmin>
```

As you can see, when appropriate the properties and the methods on the `HEALPix` class return Astropy high-level classes such as `Quantity`, `Longitude`, and so on.

For example, the `healpix_to_lonlat()` method can be used to convert HEALPix indices to `Longitude` and `Latitude` objects:

```>>> lon, lat = hp.healpix_to_lonlat([1, 442, 2200])
>>> lon
<Longitude [ 0.83448555, 1.63624617, 0.4712389 ] rad>
>>> lat
The `HEALPix` class includes methods that take or return `SkyCoord` objects (we will take a look at this in the Celestial coordinates section).