example of using my extra context hook in django-olwidget to add custom base layers

multi_layer_map.html

<div id="{{ id }}"></div>
{{ layer_html|join:"" }}
<script type="text/javascript">
    var olwidget_map_{{id}} = new olwidget.Map("{{ id }}", [
            {{ layer_js|join:"," }}
        ], 
        {{ map_opts|safe }}
    );
    var extra_layers = {{ extra_base_layers|default:"[]"|safe }};
    for (var i=0, len=extra_layers.length; i < len; ++i) {
       olwidget_map_{{id}}.addLayer(new OpenLayers.Layer[extra_layers[i].class] (
          extra_layers[i].name, extra_layers[i].url,
          extra_layers[i].params, extra_layers[i].options));
    };
    olwidget_map_{{id}}.initCenter();

    // Open up the editing control by default.
    for (var i = 0; i < olwidget_map_{{id}}.controls.length; i++) {
        if (olwidget_map_{{id}}.controls[i] && olwidget_map_{{id}}.controls[i].CLASS_NAME == "olwidget.EditableLayerSwitcher") {
           olwidget_map_{{id}}.controls[i].setEditing(olwidget_map_{{id}}.vectorLayers[0]);
           break;
        }
    }
</script>