Add basemaps GUI and update image

docs/gui/basemaps.md

@@ -0,0 +1,21 @@
+# Basemaps
+
+All [versions](../gui/versions.md) have one or more basemaps (sometimes referred to as background maps). A basemap is made up of a layer source and a basemap definition.
+
+### Creating the layer source
+
+A basemap first requires a [layer source](../gui/layers.md) to be created that defines where the layer comes from.
+
+The easiest way to create a layer source and then a basemap is to use the [layer wizard](../gui/layers.md#add-a-new-layer-using-the-wizard). This will take you through the steps to create a layer source and then present you with the basemap configuration interface.
+
+### Configuring a basemap
+
+A basemap is similar to a layer, but with a few less options.
+
+- Name: The friendly name for the basemap
+- Minimum viewable zoom level: This is the furthest zoomed out this basemap can be rendered at. This will restrict the map from being zoomed out any further than this
+- Maximum viewable zoom level: This is the furthest zoomed in this basemap can be rendered at. This will restrict the map from being zoomed in any further than this
+- Preview image URL: A URL to a preview image that will appear in the basemaps panel. This can be any valid image file. We recommend it be around 800x200 pixels
+- Max bounds: The maximum extent that this basemap should render to. Can be used to prevent basemaps being shown outside of your area of interest
+
+Once created, the basemap can be added to versions just like any other.