Mapping With Drupal - Alan Palazzolo [25]
OpenLayers layers
Layers can be put into two categories. The base layer contains the underlying map, which is usually the tile set, such as MapQuest’s Open Aerial tiles; there is only one of these displayed at a time. The overlay layers contain all your added data, such as icons marking businesses, compost facilities, or public toilets; there can be multiple overlay layers displayed on one map. The base layer can be thought of as the map layer; the overlay layer can be thought of as the data layer.
The OpenLayers module comes with several map layers, including four types of Google map tiles (normal, satellite, hybrid, and physical), three types of Yahoo! map tiles (satellite, street, and hybrid), three types of Bing map tiles (satellite, street, and hybrid), and four types of OpenStreetMap tiles. You can see these on the Layers Configuration page at admin/structure/openlayers/layers. Other Drupal modules, such as MapBox, add even more map layers. Adding further map layers is discussed in Chapter 6. For the examples in this chapter we are just going to use one of the default map layers.
The data overlays are more critical to understand because this is where you will be able to add your Drupal data and then put it on a map. By utilizing Views, you can create many data overlays to go on a single map. Data overlays can also come from an external source, such as a KML file, but this is managed through the OpenLayers Layers interface.
To summarize, there are four stages in creating a map using the OpenLayers module:
Create a data layer to receive the user-supplied data about Drupal groups.
Create a Map to display this data layer over a map layer.
Create a page to display your Map.
Tweak the Styles and Behaviors to beautify how your data appears on your Map.
The most common way to create a data layer is using the Views module. In Geofield Module we created some Drupal user groups. We will use Views and OpenLayers to display all of these on a map.
From the Views page add a new view, admin/structure/views/add.
For the “View name,” enter Drupal groups.
Tick the “Description” checkbox and enter this description: Drupal groups data layer for a map. This description will show up later in the user interface and is helpful there.
In the “Show” section, leave “Content” selected from the first drop-down. Change the “type” drop-down to “User Group.” Leave the “sorted by” drop-down set to “Newest first.”
NOTE
If you do not see the “User Group,” make sure that you created this content type in Geofield Module.
Uncheck the “Create a page” checkbox. At this stage we are creating a data layer, not a page or block.
Click the “Continue & edit” button.
Click the “Add” button (circled in red in Figure 4-2) and click on “OpenLayers Data Overlay” from the list of displays that shows.
Figure 4-2. Adding a display to a View
Enter a Title for the View, such as Drupal groups data layer.
NOTE
The Views module allows you to create multiple displays in one View. In this example we are only creating an “OpenLayers Data Overlay” display. Other displays include a Page, Block, or Feed. If you have multiple displays in one view, you need to be aware of whether you are changing a setting for one display or all displays. For simplicity, we will only have one display in this View, so for this and all following settings the changes that you make can be applied to all displays.
In the “Fields” section of the Views configuration form we need to add the fields that contain the location information for our “User Group” content type. This is the information that OpenLayers is going to extract from our stored data, interpret, and use to display the data layer of our map. Click the “add” button (circled in red in Figure 4-3).
Figure 4-3. Adding a field to a display
On the list of fields that shows, find the field labelled “Content: Group location” and select it, then click the “Add and configure fields” button, shown in Figure 4-4.
Figure 4-4. Adding the Group location field
On the “Configure