# projections Property

Vega `projections` map longitude and latitude data to projected `x` and `y` coordinates. When working with geospatial data in OmniSci, you can use projections to define geographic points and regions.

General `projections` property JSON format:

```
"projections": [
       {
         "name": "<projectionName>",
         "type": "<projectionType>",
         "bounds": {
               "x": [<minLong>,<maxLong>],
               "y": [<minLat>,<maxLat>]
         }
       }
]
```

When you specify a projection, you must reference it in the [Marks Property](https://docs.heavy.ai/v8.3.0/apis-and-interfaces/vega/vega-reference-overview/marks-property) using the `transform` object. For example, if you define the projection `my_mercator_projection`:

```
"projections": [
{
   "name": "my_mercator_projection",
   "type": "mercator",
   "bounds": {
     "x": [-120.0, 120.0],
     "y": [-20.0,20.0]
   }
 }
 ]
```

you then reference it as follows:

```
"marks": [
{
   "type": "symbol",
   "from": { "data": "fec_contributions_oct" },
   "properties": { ... elided ... }
   "transform": {
      "projection": "my_mercator_projection"
   }
 }
 ]
```

The projections specification has the following properties:

| Property | Data Type | Required | Description                                                                                                                                                                           |
| -------- | --------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `name`   | string    | X        | User-assigned name of the projection.                                                                                                                                                 |
| `type`   | string    | X        | <p>Projection type. Currently supported types:</p><ul><li><code>mercator</code>: Mercator map projection.</li></ul>                                                                   |
| `bounds` | object    |          | <p>Specifies the longitude and latitude bounding box for the projection. Default values:</p><ul><li><code>x</code>: \[-180.0, 180.0]</li><li><code>y</code>: \[-85.0, 85.0]</li></ul> |

### Example <a href="#example" id="example"></a>

Use Vega projection `projection` alongside array columns:

```
{
      "width": 1024,
      "height": 1024,
      "data": [
              {
                      "name": "table",
                      "sql": "SELECT rowid, coords[1] as x, coords[2] as y FROM cities WHERE coords[1] BETWEEN $minLon AND $maxLon AND coords[2] BETWEEN $minLat AND $maxLat"
              }
      ],
      "projections": [
      {
              "name": "projection",
              "type": "mercator",
              "bounds": {
              "x": [-120.0, 120.0],
              "y": [-20.0, 20.0]
              }
      }
      ],
      "scales": [
      ],
      "marks": [
              {
                      "type": "symbol",
                      "from": {"data": "table"},
                      "properties": {
                              "shape": "circle",
                              "xc": {
                                      "field": "x"
                              },
                              "yc": {
                                      "field": "y"
                              },
                              "fillColor": "darkblue",
                              "width": 25,
                              "height": 25
                      },
                      "transform": {
                              "projection": "projection"
                      }
              }
      ]
}
```


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