Table of Contents for
OpenLayers 3.x Cookbook - Second Edition

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition OpenLayers 3.x Cookbook - Second Edition by Antonio Santiago Perez Published by Packt Publishing, 2016
  1. Cover
  2. Table of Contents
  3. OpenLayers 3.x Cookbook Second Edition
  4. OpenLayers 3.x Cookbook Second Edition
  5. Credits
  6. About the Authors
  7. About the Reviewer
  8. www.PacktPub.com
  9. Preface
  10. What you need for this book
  11. Who this book is for
  12. Sections
  13. Conventions
  14. Reader feedback
  15. Customer support
  16. 1. Web Mapping Basics
  17. Creating a simple fullscreen map
  18. Playing with the map's options
  19. Managing the map's stack layers
  20. Managing the map's controls
  21. Moving around the map view
  22. Restricting the map's extent
  23. 2. Adding Raster Layers
  24. Using Bing imagery
  25. Using OpenStreetMap imagery
  26. Adding WMS layers
  27. Changing the zoom effect
  28. Changing layer opacity
  29. Buffering the layer data to improve map navigation
  30. Creating an image layer
  31. Setting the tile size in WMS layers
  32. 3. Working with Vector Layers
  33. Adding a GML layer
  34. Adding a KML layer
  35. Creating features programmatically
  36. Exporting features as GeoJSON
  37. Reading and creating features from a WKT
  38. Using point features as markers
  39. Removing or cloning features using overlays
  40. Zooming to the extent of a layer
  41. Adding text labels to geometry points
  42. Adding features from a WFS server
  43. Using the cluster strategy
  44. Reading features directly using AJAX
  45. Creating a heat map
  46. 4. Working with Events
  47. Creating a side-by-side map comparator
  48. Implementing a work-in-progress indicator for map layers
  49. Listening for the vector layer features' events
  50. Listening for mouse or touch events
  51. Using the keyboard to pan or zoom
  52. 5. Adding Controls
  53. Adding and removing controls
  54. Working with geolocation
  55. Placing controls outside the map
  56. Drawing features across multiple vector layers
  57. Modifying features
  58. Measuring distances and areas
  59. Getting feature information from a data source
  60. Getting information from a WMS server
  61. 6. Styling Features
  62. Styling layers
  63. Styling features based on geometry type
  64. Styling based on feature attributes
  65. Styling interaction render intents
  66. Styling clustered features
  67. 7. Beyond the Basics
  68. Working with projections
  69. Creating a custom control
  70. Selecting features by dragging out a selection area
  71. Transitioning between weather forecast imagery
  72. Using the custom OpenLayers library build
  73. Drawing in freehand mode
  74. Modifying layer appearance
  75. Adding features to the vector layer by dragging and dropping them
  76. Making use of map permalinks
  77. Index

Restricting the map's extent

Often, there are situations where you are interested in showing data to the user, but only for a specific area, which your available data corresponds to (a country, a region, a city, and so on).

In this case, there is no point in allowing the user to explore the whole world, so you need to limit the extent the user can navigate.

In this recipe, we present some ways to limit the area that a user can explore. You can find the source code in ch01/ch01-map-extent/. We'll end up with a restricted extent of the USA like in the following screenshot:

Restricting the map's extent

How to do it…

  1. Create the HTML to house the map and include the OpenLayers dependencies.
  2. Create your JavaScript file and set up a geographic extent:
    var extent = ol.proj.transformExtent(
  [-125.0011, 24.9493, -66.9326, 49.5904],
  'EPSG:4326', 'EPSG:3857'
);
  3. Create the map instance with some layers and a restricted view, as follows:
    new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.Stamen({
        layer: 'watercolor'
      })
    }),
    new ol.layer.Tile({
      source: new ol.source.Stamen({
        layer: 'terrain-labels'
      }),
      extent: extent
    })
  ],
  target: 'js-map',
  view: new ol.View({
    zoom: 6,
    minZoom: 5,
    center: [-12100000, 3400000],
    extent: extent
  })
});

How it works…

When you launch this recipe on your web browser, you'll notice that you cannot pan outside the restricted extent. Let's take a look at how this was accomplished:

var extent = ol.proj.transformExtent(
  [-125.0011, 24.9493, -66.9326, 49.5904],
  'EPSG:4326', 'EPSG:3857'
);

We've put together a bounding box which covers the United States. This extent is in longitude and latitude coordinates, but the map view is in a different projection (EPSG:3857). We need to convert our longitude and latitude extent into the map view projection.

The ol.proj.transformExtent projection helper method provides such a utility. We pass in the array of coordinates as the first parameter. The second parameter informs OpenLayers that the provided coordinates are in longitude and latitude (EPSG:4326). The final parameter tells OpenLayers what we'd like the coordinates to be converted into (EPSG:3857). This returns with an ol.Extent array we can use on the map. We store this array in a variable, namely extent, as we'll use it in a few places around the code:

new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.Stamen({
        layer: 'watercolor'
      })
    }),
    new ol.layer.Tile({
      source: new ol.source.Stamen({
        layer: 'terrain-labels'
      }),
      extent: extent
    })
  ],

When we create the new map instance, we make use of the Stamen tile services. The background layer is made up of the watercolor layer, and the foreground layer is made up from the terrain-labels layer.

For the terrain-labels layer, we restrict the extent of the layer with our custom bounding box. It means that this layer will not request for tiles outside this extent.

view: new ol.View({
  zoom: 6,
  minZoom: 5,
  center: [-12100000, 3400000],
  extent: extent
})

When we create the view, we pass our bounding box into the extent property of the view. Passing the extent to view is where the navigation restriction gets enforced. If we hadn't passed the extent to view, the user could pan around the map as they wish.

We also set minZoom to 5, which accompanies the extent restriction quite well. It prevents the user from zooming far out and beyond the USA (our extent). This retains the user within the points of interest.

See also

  • The Moving around the map view recipe