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6. Layers

6.1. Introduction

Geographical data are most often apprehended as thematic layers: you may have a layer "Rivers", a layer "Aerial view", a layer "Average income", just to cite a few examples. Now the basic purpose of any viewer is to make these data available to users by allowing navigation within a layer as well as comparison between layers. A way to organize the layers is thus mandatory if an user-friendly application is to be developed. In CartoWeb, the files that contain the configuration instructions for the layers are on the server-side, in the directory server_conf/<myMap>. Usually this directory is part of a project.

CartoWeb is based on the geographical engine Mapserver. The Mapserver documentation http://mapserver.gis.umn.edu/doc.html is an integral part of the CartoWeb doc. To be concise, you have to know how to write a mapfile if you want to use CartoWeb. So it doesn't come as a surprise that a mapfile, myMap.map, is included in the <myMap> directory, together with its annexes (typically a symbol file myMap.sym, a directory etc for the required fonts, the graphic file used as keymap background, maybe also data files).

We'll see that some functionalities of CartoWeb require small changes of the mapfile content. But most of the configuration is done in the file layers.ini.

The file myMap.ini sets the required plugins and the initial state of the map. Its content is described in Chapter 4, Configuration Files

6.2. Hierarchy of Layers and Rendering

Contrary to Mapserver itself, CartoWeb supports an arbitrarily complex hierarchy of layers and different rendering options. The notion of LayerGroup makes it possible.

6.2.1. Layers and LayerGroups

There are two types of "layers-like objects" in layers.ini : Layers and LayerGroups. They play fairly different roles and consequently have different possible attributes. Layers have a 1-to-1 correspondance to Mapserver layers (as defined in the layers.map), while LayerGroups group together atomic Layers or other LayerGroups.

6.2.2. Layers Options

As seen before, the Layer object maps directly to a layer in the mapfile. By default, all layers in the mapfile are made available as a Layer in the layers.ini, with an identifier having the same name as the name of the mapserver layer. Thus, if you have the following option in your mapfile:

  NAME "my_layer"
  TYPE line 

This is equivalent as writing the following configuration in the layers.ini:

layers.my_layer.class = Layer 
layers.my_layer.label = my_layer
layers.my_layer.msLayer = my_layer


If you don't need special parameters (see below) for your layer then you can avoid adding it in the layers.ini

However, if you want these layers to appear in the layer list, you still have the responsibility to affect them a parent layer, using the children property of the LayerGroup layer declarations.

Here is the syntax for the various configuration parameters of a Layer.

  • layers.layerId.className = Layer : defines the object as a Layer; layerId is a string that uniquely identifies the object. The general rules of syntax for a .ini file must be respected in the choice of the layerId (e.g. no '-' are allowed).
  • layers.layerId.msLayer = string : name of the corresponding Mapserver layer in the mapfile
  • layers.layerId.label = string : caption of the layer in the layer tree on the client; this is a 'raw' label, before any internationalization. The i18n scripts automatically include this label in the strings that can be translated.
  • layers.layerId.icon = filename : filename of the static picto that illustrates this Layer in the layer tree. The file is expected to be in server_conf/<mapId>/icons and a setup script launch is in most cases required. See also Section 6.4, “Layers Legends” for a description of the automatic legending process.
  • layers.layerId.link = url : provides a link for the layer (e.g. to some metadata); makes the caption in the tree clickable.

6.2.3. LayerGroups Options

Here is the syntax for the various configuration parameters of LayerGroups. Note that a special LayerGroup with layerId=root must be present. Unsurprisingly, it is the root (top level) of the hierarchy. It doesn't appear in the visible tree.

  • layers.layerId.className = LayerGroup : defines the object as a LayerGroup; layerId is a string that uniquely identifies the object. The general rules of syntax for a .ini file must be respected in the choice of the layerId (e.g. no '-' are allowed).
  • layers.layerId.children = list of layerIds : comma-separated list of layerIds; these children may be Layers or other LayerGroups.
  • layers.layerId.children.switchId = list of layerIds : comma-separated list of layerIds, when using switching (see Section 6.2.4, “Children Switching”). This option cannot be used together with simple children option.
  • layers.layerId.aggregate = true|false : if true, the children objects are not listed in the tree and not individually selectable. Default is false.
  • layers.layerId.label = string : caption of the layer in the layer tree on the client; this is a 'raw' label, before any internationalization. The i18n scripts automatically include this label in the strings that can be translated.
  • layers.layerId.icon = filename : filename of the static picto that illustrates this Layer in the layer tree. The path is relative to myMap.ini. See also Section 6.4, “Layers Legends” for a description of the automatic legending process.
  • layers.layerId.link = url : provides a link for the layer (e.g. to some metadata); makes the caption in the tree clickable.
  • layers.layerId.rendering = tree|block|radio|dropdown : indicates how to display the LayerGroup children.
    • tree (default value): children layers are rendered below the LayerGroup with an indentation. If children are not declared as "frozen" or "hidden" they will be preceded by a checkbox input. A node folding/unfolding link is displayed before the LayerGroup.
    • radio: quite similar to the "tree" rendering with "radio" buttons replacing checkboxes. Only one child layer can be selected at a time.
    • block: children layers are separated as blocks (separation medium depends on the template layout). Note that the rendering will be applied to the children, not to the LayerGroup itself, which is not displayed at all.
    • dropdown: as for block rendering, the LayerGroup is not displayed. Its children are simply rendered as an HTML "simple select" options list. If the selected child layer cannot be determined using posted or session-saved data, first child (according to the layers.layerId.children list order) is selected. If any, only the selected child layer's own children are displayed under the dropdown list.
  • layers.layerId.metadata.minScale (resp. maxScale): one may specify a numerical minimal (resp. maximal) scale for the given LayerGroup. This parameter has absolutely no effect on Mapserver behavior and is only used to display out-of-scale icons and links in the layers tree. For more info about layers.ini metadata parameters, see Section 6.3.2, “Metadata in layers.ini.

6.2.4. Children Switching

Children switching is useful to define several lists of children for one layer group. The children that will be displayed is choosen by a special parameter : the switch ID.

Switch IDs and labels are listed in file layers.ini. In default test environment, a dropdown is constructed using this list and displayed in the GUI.

switches.switch1.label = Switch 1
switches.switch2.label = Switch 2
switches.switch3.label = Switch 3

Then, each layer group that needs to change its children depending on the switch ID may add this ID as a suffix to the children option.

layers.layerId.className = LayerGroup
layers.layerId.children.switch1 = layer1, layer3
layers.layerId.children.switch2 = layer2, layer3
layers.layerId.children.switch3 =

Special suffix default can be used to define a default children list :

layers.layerId.className = LayerGroup
layers.layerId.children.switch2 = layer2, layer3
layers.layerId.children.default =

The following layer group definitions are equivalent :

layers.layerId.className = LayerGroup
layers.layerId.children.default = layer4
layers.layerId.className = LayerGroup
layers.layerId.children = layer4

6.3. Metadata in Mapfile and layers.ini

Metadata are (keyword, value) pairs which can be associated to a MapServer layer in the mapfile, or to a Layer or LayerGroup in the layers.ini configuration file. These metadata are used in several different contextes, such as layer specific configuration, security handling, ... The metadata related to the functionalities of CartoWeb are described in the documentation of the corresponding plugins.

6.3.1. Metadata in Mapfiles

Specifying metadata in mapfiles is based on the standard MapServer syntax. For instance:

  NAME "my_layer"
    "exported_values" "security_view,some_specific_parameter"
    "security_view" "admin" 
    "some_specific_parameter" "value"
    "id_attribute_string" "FID|string" 
    "mask_transparency" "50"
    "mask_color" "255, 255, 0"
    "area_fixed_value" "10"

The metadata key exported_values is a bit special: It gives the list of metadata keys (coma separated), which will be transmitted to the client. This is required for the metadata keys describing layer security for instance, as they are used on the CartoClient.

6.3.2. Metadata in layers.ini

The configuration file layers.ini may also contain metadata (key, value) pairs. This is needed for LayerGroup objects, as these have no counterparts in the mapfile. For simple layers, the metadata specified in the layers.ini take precedence over the values from the mapfile.

For each layer object in the layers.ini file, the following syntax is used to set metadata:

layers.layerId.metadata.METADATA = value

For instance:

layers.group_admin.className = LayerGroup 
layers.group_admin.children = grid_defaulthilight 
layers.group_admin.metadata.security_view = admin


It is possible to specify minScale and maxScale attributes as layers.ini metadata for layerGroups items. The equivalent mapfile metadata is not available for layers. In that case, simply use mapfile MINSCALE and MAXSCALE attributes.

6.3.3. Using the metadata fields in templates (layers.tpl)

Metadata declared in mapfiles or layers.ini can be used in the layers.tpl Smarty templates using the following notation:

{capture name=caption}
{$element.layerLabel} <a

As we can see in the previous example, metadata values can be used through the layerMeta property of the $element Smarty variable. Typical usage of this feature is to render for instance several HTML links for each layers.

6.4. Layers Legends

CartoWeb includes a mechanism for the automatic generation of legends. If desired, an icon is drawn for each class of the layers. There are two conditions that must be fulfilled to make it work :

1. The mechanism must be enabled by setting

autoClassLegend = true

in layers.ini.

2. Each class (or more precisely each class that should appear in the legend) must have a name. Here an example :

  NAME "spur_spurweite"
  TYPE line

    NAME "Normalspur (1435 mm)"
    EXPRESSION ([MM] = 1435)
      COLOR 0 0 255 # blue

#   NAME "Meterspur (1000 mm)"
    EXPRESSION ([MM] = 1000)
      COLOR 255 0 0 # red

    NAME "Schmalspur (< 900 mm)"
    EXPRESSION ([MM] < 900)
      COLOR 128 0 128 # lila


In this case, the second class would not appear in the legend, because the NAME is commented out.

Provided that no static icon is defined for a layer in layers.ini, the icon of the first visible class is used for the layer.

Legend icons are also used when exporting maps in PDF (see Chapter 12, PDF Export). Standard legend icons are used by default, which means that they may seem pixelized when printing a 300 dpi map. To resolve this issue, the following parameter can be set in layers.ini:

legendResolutions = 96, 150, 300

Each resolution must correspond to one of those set in PDF Export configuration file. This file is described in Section 12.2.1, “General Configuration”.

6.5. WMS Layers Legends

Mapserver could act like a WMS client and retrieved layer from distant WMS server. In this specific case, layers legends could be retrieved directly from a distant server with SLD support (getLegendGraphic method).

You must also add a metadata on each WMS layer to retrieve its legend icon: wms_legend_graphic

Here is an example:

  NAME 'prov_boundary'

  CONNECTION 'http://www2.dmsolutions.ca/cgi-bin/mswms_gmap?'
    'wms_srs'             'EPSG:4326'
    'wms_name'            'prov_bound'
    'wms_server_version'  '1.1.1'
    'wms_format'          'image/png'
    'wms_legend_graphic'  'true'

6.6. Auto Layers

In some cases, it may be useful to generate several layers out of a single "template" layer. An example would be floors : each floor must be displayed with the same color, etc. but the data source is different (different shapefile or different where clause for a database layer). In CartoWeb, it is possible to add PHP code into mapfiles. True mapfiles are then generated by a batch script. The generated layers are called "Auto Layers".

6.6.1. Auto Layers in layers.ini

First, you have to declare the list of auto layers indexes. Indexes will be used as suffixes for generated layers :

autoLayersIndexes = index1, index2

Then you can use auto layers just as other layers. In this exemple, an auto layer myAutoLayer_ was declared in the mapfile template (see Section 6.6.2, “Mapfile Templates”).

layers.layer1.className = LayerGroup
layers.layer1.children = layer2, myAutoLayer_index1

layers.layer2.className = LayerGroup
layers.layer2.children = myAutoLayer_index2 

6.6.2. Mapfile Templates

Mapfile templates for auto layers are PHP files. The main template must be called mapId.map.php. If this file exists, then CartoWeb assumes that auto layers generation is used. If the file does not exists, CartoWeb looks for a standard mapId.map.

The following functions are predefined and can be used in mapfile templates :

  • printLayer($name, $contents) : adds a new auto layer. The name is the final name of the layer without the index suffix. Contents include Mapserver layer definition with PHP code for parts that will be different for each instance of auto layer
  • printIndex() : adds the current auto layer index. Must be used in auto layer contents
  • printName() : adds the current auto layer full name. Must be used in auto layer contents
  • getIndex() : returns the current auto layer index. It can be useful for instance in conditional statements. Must be used in auto layer contents
  • includeFile($path) : adds the content of another PHP mapfile template

Here is an example :

  NAME "MyMapfile"
  EXTENT -10 -10 10 10
# ...




  # This is my auto layer with index <?php printIndex(); ?>
    NAME <?php printName(); ?>
# ...
      NAME "MyClass"
        COLOR <?php if(getIndex() == 'index2') print "200 200 255";
                                          else print "255 153 102"; ?>



6.6.3. Batch Script

Script makemaps.php located in directory scripts generates mapfiles out of mapfile templates for all projects. Mapfiles are generated in the same directory. The script must be called once during installation and then each time a change is made to the mapfile templates.

It uses filelayers.ini to find out which auto layers are needed. For instance, with the following layers.ini, myAutoLayer_index3 won't be generated.

autoLayersIndexes = index1, index2, index3
layers.layer1.className = LayerGroup
layers.layer1.children = layer2, myAutoLayer_index1

layers.layer2.className = LayerGroup
layers.layer2.children = myAutoLayer_index2 

At least one file is generated. Its name is auto.mapId.all.map and it contains all auto layers used in file layers.ini. When children switching is used (see Section 6.2.4, “Children Switching”), one mapfile is generated per switch. One more is generated for special switch default. This way, only auto layers used with the current switch are actually loaded at runtime. Mapfile auto.mapId.all.map is still generated.

In the following example, 4 mapfiles are generated :

autoLayersIndexes = index1, index2, index3, index4
switches.switch1.label = Switch 1
switches.switch2.label = Switch 2

layers.layer1.className = LayerGroup
layers.layer1.children.switch1 = layer2, myAutoLayer_index1
layers.layer1.children.default = layer2, myAutoLayer_index2

layers.layer2.className = LayerGroup
layers.layer2.children = myAutoLayer_index4 
  • auto.mapId.all.map : contains all layers used in layers.ini, ie. layers myAutoLayer_index1, myAutoLayer_index2 and myAutoLayer_index4
  • auto.mapId.switch1.map : contains layers used when Switch 1 is selected, ie. layers myAutoLayer_index1 and myAutoLayer_index4
  • auto.mapId.switch2.map : contains layers used when Switch 2 is selected, ie. layers myAutoLayer_index2 and myAutoLayer_index4
  • auto.mapId.default.map : contains layers used when no switch is selected, ie. layers myAutoLayer_index2 and myAutoLayer_index4

6.7. Layer Reorder Plugin

Ability to reorder displayed layers could be appreciated by end user. And so, even if your map is well designed with largest features layers on bottom and smallest on top, and/or even with well used transparent properties. The plugin layerReorder , is designed to do so. Layers could be reorder on the displayed stack to improve visibility of one layer.

Each layer defined in the mapfile and currently selected in legend menu (and only them) will be displayed in the reorder menu list.

6.7.1. Plugin activation

To activate the plugin, add it to loadPlugins from Both CartoClient and CartoServer configuration files: client_conf/client.ini and server_conf/<mapId>/<mapId>.ini. For instance:

loadPlugins = layerReorder

6.7.2. Layer exclusion

If you want to exclude some layers and then not allow them to be reordered, have a look on client_conf/layerReorder.ini. You will be able to exclude some layers and to choose to keep them on bottom (or on top). To do so, use the following configuration parameters:

  • topLayers: list of all layerIds to keep on top of the genererated map (LayerIds must be comma separated).
  • bottomLayers: same as previous one, but obviously keep these layerIds on bottom. Useful for example with a raster background layer.

6.7.3. Transparency selector

You could also add a transparency selector on each layer displayed with this plugin. End user will so be able to choose a different transparency level for each displayed layer.

To activate it, set enableTransparency to true in client_conf/layerReorder.ini.

Default transparency selector values are : 10%, 20%, 50%, 75% and 100%. You could also customize transparency values available in this selector, with a comma separated value in transparencyLevels. A transparency value is a integer between 1 to 100 ; with 100 mean an opaque layer as 1 mean a nearly invisible one.

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