# Map Parameter
<flow-map-parameter> Map parameters supply additional parameters to map data sources and map data joins.
The Map Parameter component is used to supply parameters to parameterized map data sources and map data joins. Multiple parameters can be set by specifying multiple map parameters.
The value of the map parameter is a reactive expression. Changes to the value trigger a reload of the map data source or map data join. Internally, map parameters are added to the query string of the underlying data request.
# Examples
# Displaying Parameterized Vector Map Tiles
In the example below air quality data for London is displayed. The map data source is a parameterized Flo.w vector tile source, which takes an no2_filter parameter. Data points are returned where no2 > no2_filter. Adjust the slider to reactively set the no2_filter value and trigger an update of the data.
Note that in this simple example, filtering is performed server-side. Client-side filtering can also be performed at the map layer level by specifying the filter attribute of the Map Layer component.