title: $:/plugins/tiddlywiki/geospatial/docs/geodifference
caption: geodifference operator
tags: $:/tags/GeospatialDocs

!! `geodifference` operator

The `geodifference` operator calculates the difference between two or more [[GeoJSON Polygon Features|GeoJSON Polygon Feature]].

Each input list item is interpreted as a [[GeoJSON Polygon Feature Collection]] containing polygons.

```
[geodifference[]]
```

!! `geolookup` operator

The `geolookup` operator identifies the polygon(s) within a [[GeoJSON Polygon Feature]] that correspond to a particular point, and returns the JSON properties of that polygon.

Each input list item is interpreted as a [[GeoJSON Point Feature]] and the operand is interpreted as a [[GeoJSON Polygon Feature Collection]].

For example, here we lookup the point 100.5,0.5 in the [[GeoJSON Polygon Feature Collection]] stored in the tiddler `TestData` and then extracts the indexes `0` and `animal` from the resulting JSON:

```
<$text text={{{ [geopoint[100.5],[0.5]geolookup{TestData}jsonget[0],[animal]] }}}/>
```

!! `olc-decode` operator

The `olc-decode` operator converts an [[OpenLocationCode|https://github.com/google/open-location-code]] shortcut into the [[GeoJSON Point Feature]] at its centre or the [[GeoJSON Polygon Feature]] representing the bounds of the area identified by the input code.

```
[olc-decode:bounds[9C3WQP2R+QV]]
[olc-decode:point[9C3WQP2R+QVH]]
```

!! `olc-encode` operator

The `old-encode` operator converts separate latitude and longitude numbers into an [[OpenLocationCode|https://github.com/google/open-location-code]] shortcut code with a specified length (defaults to 11 characters).

```
[olc-encode[51.751944],[-1.257778]]
[olc-encode[51.751944],[-1.257778],[11]]
```