Web GIS concepts for GIS users

Most people love the quality of information from, ease of use, and performance of Google Earth, Google Maps, and Microsoft Bing Maps. If you ask most people what they like, they would likely tell you about the high-resolution imagery, the ability to easily locate places of interest (that is, to geocode addresses), the ease of exploring the map in 2D and 3D, the responsiveness, and the ability to add their own information as layers (that is, mash up).

Dig a little bit deeper from a GIS perspective, and you will find some very good lessons and ideas that you can implement with ArcGIS to build and serve your own digital maps and globes on the Web. These lessons can help simplify and enrich your users' experiences.

• The primary value of Google Earth, Google Maps, and Bing Maps for GIS is as a basemap. These online Web maps provide a common basemap framework onto which geographic information can be overlaid and used. Sometimes (with the proper licensing and permissions to use this commercial content), your organization can use these Web maps as basemaps in your GIS applications.

  In many other situations for a host of reasons, you will need to think about publishing and serving your own GIS basemap.

• Most GIS applications should include a basemap onto which operational information is overlaid. All digital map applications require a strong map base on which to operate. Much like Google Earth and Bing Maps, your GIS base map provides a framework on which your operational information can be overlaid, viewed, and used.

  Each basemap should support specific requirements. For example, your basemap can be tailored to the specific application domain that reflects your organization's work and mission.

• There is no single universal basemap, but there are a number of standard basemaps that are commonly used (and that you can leverage in your own GIS applications). No single basemap can work for all situations and all scenarios. But, the basemap services provided by Google, Microsoft, and ESRI provide some that are in wide use. They can support a broad range of application scenarios, and many users think of them as standard basemaps for their applications.

  So it goes without saying that there are many cases where it will make sense to leverage an existing basemap service on the Web. For example, you can overlay and work with your operational content and observations on top of Google Earth, Google Maps, Bing Maps, or ArcGIS Online basemaps. See Basemap alternatives for more information about using existing Web maps for your GIS applications.

  However, in just as many other cases, these existing Web maps will not support your organization's work and mission. You will need to design, publish, and maintain your own basemap for your area of interest. When you create a basemap, it can provide a more focused context and include data themes that support your daily operations. Many GIS organizations publish and support a range of basemaps for their own use. These include basemap frameworks for parcels and cadastral work, hydrology, geology, demographic and population work, land bases for utilities, topographic maps for recreation and environment, forest maps, engineering maps, construction site maps, historical maps, charts for nautical and aeronautical navigation, emergency response maps, and a myriad of other application examples. The Map Templates page in the ArcGIS Resource Center offers a variety of downloadable samples that can give you ideas of how to start building your own basemap.

• In most cases, your basemap should be multiresolution. Your basemap should know how to display itself across the range of map scales that are needed to support your work. For example, what will your basemap look like for your complete study area? What are the other map scales at which your users will perform their daily work? As you zoom in on your basemap, what are the map elements and how are they to be portrayed at each map scale?

  Your basemap should be designed to portray itself appropriately at a range of supported map scales (like the behavior that you see in ArcGIS Online, Google Earth, and Bing Maps).

  Some of the map scales represented in the multiresolution street map that can be accessed from http://arcgisonline.esri.com

  It is interesting to note that a typical worldwide street map on the Web from Google, Microsoft, or ESRI is actually a series of 15 to 20 integrated maps. There is one map that is used to portray streets at each map scale. At a very generalized national or global extent, the map scale is around 1:150 million; for large parts of North America around 1:50 million; and in cities, various map scales are supported that can be zoomed in and used at a map scale as large as 1:2,000. If your GIS is primarily focused on a city or urban area, you will probably have map applications that work within about 6 to 10 map scales that range from around 1:500,000 and down to a zoomed-in, detailed map scale that can be as large as 1:1,000 or 1:600. If your GIS deals with regional applications, you may have maps that work for 6 to 10 map scales that start around 1:2.5 million and can zoom in to a detailed map scale of around 1:10,000.

• Your basemap may require more detailed coverage in portions of your area of interest. Some basemaps need to provide higher levels of detail in populated areas. This often happens for national, state, and regional GIS organizations. For example, you may have a nationwide map that includes larger map scales for cities and urban areas.

  Example of a nationwide, multiresolution basemap. The red areas are urban areas in which the map zooms into much larger map scales than in rural areas outside the red zones.

  Often, you can think about extending the ArcGIS Online basemap services using your own authoritative, more detailed, up-to-date content for your study area. At zoomed-out map scales, your basemap might start with ArcGIS Online services, but transform into your map services as you zoom into your study area.
• For improved performance, you should use a map cache for your basemap. Basemaps provide an operational framework and context for your GIS operations. In most cases, the basemap information will change less frequently than your operational information. You can precompute the basemap to support optimum performance and scalability.

  This requires a design for building your map cache. See Planning a map cache for more information. It's also important to maintain your basemap services over time. You'll need well-defined procedures to keep your basemap up-to-date. Using ArcGIS, you can set up and automate workflows to maintain your basemap cache as its contents are updated over time. It is useful to build a set of back-office procedures and scripts that can be used to automate map updates to your basemap cache. Each map tile is recomputed as data updates are made within a map tile. See Automating cache creation and updates with geoprocessing for more information.

• Many GIS basemaps can be 3D. Most users will focus initially on a 2D version of their basemaps, but over time, there could be a 3D version as well. Many 2D basemaps can be migrated to 3D by overlaying the 2D content onto digital terrain. This provides a framework for adding 3D representations, such as 3D features that can be positioned on the earth's surface, as well as for depicting subsurface structures.

  You can build globe services by adding your 2D map into an ArcGlobe session and publishing the globe document as an ArcGIS Server globe service.