10 Oct 2011

Development: The Fall of the Tiled Map Image

Pregenerated tiled map images as used by Google Maps, Microsoft Bing and many GIS focused vendors has been the dominant solution GIS web mapping for solutions for many years. Pregenerated tile maps were a clever and highly successful solution to the technology limitations of the time (circa 2004) however, these limitations no longer exist. Is it time for a change of approach?

The pregenerated tile image approach offered a high scale solution for fundamentally static data. It enabled browsers with poor support for vector graphics (slow VML and SVG) and slow javascript engines to deliver a seamless highly interactive user experience.The pregeneration exercise required massive processing power to create tiles and huge storage requirements to store them. Refreshing tile sets was a cumersome affair with considerable overhead. For reasonable sized areas and deep zoom levels it becomes cost prohibitive for many organizations. Replacing pregeneration with on the fly generation is too slow for a practical user experience with most tile engines. Many clever caching strategies have been used to work around this issue but they all have limitations. From an end user perspective map tiles are just images. They lack the interactive experiences possible with vector data. Tiled map images are considerably larger than their vector data equivalent and do not compress well using compression techniques available within HTTP hence, are not well suited to smaller bandwidth web environments.

Several key technology changes may help solve these issues and drive change to more modern and effective techniques:
Browser Statistics
  • HTML 5 - brings with it long awaited support for standardized vector graphics through SVG and Canvas.
  • Wide and comprehensive support for HTML 5 in modern browsers.
  • High Performance Browser Vector Graphics - both IE and Firefox now support hardware enabled vector rendering. Prior to this the practical limit for vector graphics in browsers was 500-1000 features. The new are not clear but examples exist of in excess of 10,000 features.
  • Massive performance enhancements for Javascript engines
  • Rapid adoption of more capable browser releases driven by better user experiences and increased concerns over browser security by IT teams.
  • Mobile - mobile is rapidly becoming the most important end user platform. Mobile form factors range from traditional small devices to touch tablets.
  • Dynamic data - timely near real time data has become part of a normal user experience.
  • User experience - user expectations have increased significantly and pregenerated tiles can no longer deliver.
    What will be the next generation of web mapping?
    The technology barriers and drivers above all point to a new solution - vector web mapping. Why?
    1. Better Support for Mobile - Vector graphics have significant advantages to support multiple mobile form factors. Vector graphics are available in HTML 5 compliant mobile browsers. Vector graphics are relatively small size compared with images means hence, support lower bandwidth environments. Vectors also compress well (up to 90%) using GZIP that is available within HTTP.
    2. Dynamic Data - with pregenerated tile images its impossible to adequately provide support for dynamic data. Businesses rely on rapidly changing data. Delivery of on the fly vector graphics allows real time data to be displayed. Combined with support for server push of data to browsers in HTML 5 truly dynamic data can be supported in the browser. This also enables many variations of the same map to be displayed (eg. cartography, layer visibility and subsets of features) without storage duplication.
    3. User Experience - vector graphics allow richer user experiences to be created. HTML 5 and hardware graphics support provides support for creating a practical dynamic user experience with data volumes traditionally found in GIS systems. Improved user experiences can also be achieved from the availability of vectors themselves. For example:
      • Dynamic selections and styling without return trips to the server
      • Interactivity generated by mouse movements over features
      • Rich editing interfaces
      • Vector animation for time series
      • Vector graphics are massively smaller. 7 times smaller files before compression.
      • Vector graphics are significantly faster to render. 15-20 times faster than generating an image.
      • Scalability barriers can be overcome. This removes the need for pregeneration.
    There are some examples of web mapping in vector graphics available already from small innovative companies. Google has already adopted vector graphics for its consumer focused mobile offering. An opportunity exists here for the GIS industry to take ownership of business focused web mapping back from the consumer vendors through delivery of technology focused on business needs.

    2 comments:

    1. Vector web mapping is indeed the future of current web mapping tools. Unfortunately, problems remain and the old raster-google-map culture is deeply installed... This document is interesting on this topic:
      http://dx.doi.org/10.1007/978-3-642-33024-7_7
      http://www.ahahah.eu/data/doc/gisscience2012_gaffuri_draft.pdf

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