Question:
How can I create a Thematic (Cached) layer for MapThat?
Answer:
MapThat Admin Forms allow you to create a THEMATIC type layer. These layers are not designed to create a Thematic map or Symbology within the map, but instead are used to create a ‘CACHED’ layer.
Cached layers are very useful as they allow you to utilise the geometry of a spatial layer, but will render the layer within the map far quicker. This is because the geometry for each feature is not drawn at runtime, but instead a Cached image is used. To create a Thematic type layer follow these steps:
1 – Edit an existing or make a Copy of a Spatial layer.
2 – Change the Layer Type from Spatial to be Thematic.
3 – Leave the rest of the values as they were originally, so it will be using the same Database Table, Geometry Column and Layer SQL.
4 – Now we have chosen a Thematic type layer, you can define a Tile Cache location. This should be a folder on your MapThat server that is accessible to all users.
5 – Finally, enter the following text into the VIRTUAL_DIR value for your VE_Layers record - http://servername/MapThatLocation/TileService.ashx?myID={quadkey}&Treeindex=
6 – Now within MapThat, the layer will be displayed showing the geometry objects as normal, and also allow the user to retrieve attributes via the Information Bubble. Note – as this is a Thematic Type layer the Data Table will not be available.
7 – The layer will render within the map very quickly as the layer is being drawn from Cached image tiles. If you look in the Cached folder, you will see the Cached images being saved each time you navigate to a new location.
8 – Using the Cache Control tool the user can choose whether, they use Cached Image tiles (where already available) or create new Cached images at all times.
