Catalog

What it does

The catalog lists the layers a map offers. It is a tree of named entries from the config. Tick a layer to add it to the map. Clear the tick to remove it. The legend shows the layers you have picked.

You decide the tree. It is not generated from the layer list, because config order is rarely the order readers need. Groups such as "Background," "Population," and "Historical maps" are part of the map's design.

Groups can behave in two ways, and the difference matters:

• Ordinary groups let any number of children be on at once. Ticking one changes nothing about the others.
• Single-choice groups (selectionMode: "single") allow one child at a time, which is what a background belongs in: choosing a satellite basemap should put away the street one rather than stack them. Add allowNone: true to let the reader also choose none of them.

Large catalogs can have a search box at the top of the tree. It matches labels and shows matching entries wherever they sit in the tree.

Using it

1. Open the catalog from the toolbar.
2. Expand a group and tick a layer to add it. It appears on the map and in the legend at once.
3. Type in the search box to find a layer by name without opening groups.
4. Clear the tick to remove the layer again. Any changes to the layer, such as opacity or style, belong to the legend, not here.

A catalog entry may point at a slow or unreachable service. The entry reports that state instead of failing silently.

In your own map

The tree lives on the toolbar item, as tree, and each node is one of two things: a group with children, or a leaf naming a layer with layerId.

The layerId of a leaf must match a layer in layerData.layers. That is the whole contract. The catalog does not define layers. The catalog arranges layers.

Useful keys on a node: label, children, layerId, checked (on at start), selectionMode: "single" with selectionGroup and allowNone for mutually exclusive groups, and stackOrder where a group's layers must land at a particular depth.

Extending it

The tree is read from the config through getTreeFromMapConfig, which looks for the layerTree tool item and takes its tree. A tree property set directly on the element overrides the config, so a host app can supply a catalog at runtime.

The component re-reads the tree on webmapx-config-ready, so late or replaced configurations update the catalog.