Abstract
Internet map services (IMSs) are redefining the ways in which people interact with geospatial information system (GIS) data. The driving forces behind this trend are the pervasiveness of GIS software and the emerging popularity of mobile devices and navigation systems utilizing GPS (Global Positioning System), as well as the ever-increasing availability of geospatial data on the Internet. These forces are also influencing the increasing need for temporal or real-time data. One trend that has become particularly promising in addressing this need is the development of IMS. IMS is changing the face of data access and creating an environment in which users can view, download, and query geospatial and real-time data into their own desktop software programs via the Internet. In this section, the authors will provide a brief description of the evolution and system architecture of an IMS, identify some common challenges related to implementing an IMS, and provide an example of how IMSs have been developed using real-time weather data from the National Digital Forecast Database (NDFD). Finally, the authors will briefly touch on some emerging trends in IMS, as well as discuss the future direction of IMS and their role in providing access to real-time data.
TopBackground
The origins of IMS can be traced to the geospatial data sharing initiatives of the 1990s when spatial data sharing began in earnest. In the early 1990s, the World Wide Web (WWW) and browsers altered users’ perception of the Internet. Suddenly users were able to see images and interact with the Internet through graphics and scripts and even access digital data. In the United States the creation of the National Spatial Data Infrastructure (NSDI) initiated an effort to develop standards for sharing data. By 1995 the vision for the NSDI to promote the sharing of data within the federal government and enhance sharing with state and local governments was solidified (Federal Geographic Data Committee, 1995).
Spatial data, which is defined as any data containing a locational component, have become widely available to the public through efforts of spatial data clearinghouses, governmental Web sites, and even nonprofit organizations, many of which were early NSDI initiatives. Through these spatial data clearinghouses, static spatial data were accessed traditionally via file transfer protocol (FTP). In cases such as these, the onus was on the user or client to identify, download, and manipulate data to comply with the desktop GIS environment. Temporal and real-time data have a more complex history. This type of information, which includes such diverse data types as traffic, hydrologic, and weather data, is difficult to maintain and provide access to due to its dynamic nature. For example, weather data, which encompasses everything from radar to precipitation to wind speed, are changing continuously and present the user with numerous data formats and types with which to contend (Van der Wel, Peridigao, Pawel, Barszczynska, & Kubacka, 2004). The past few years have seen advances on this front. For example, the National Weather Service (NWS) of the U.S. National Oceanic and Atmospheric Administration (NOAA) has developed several online applications that allow viewing of real-time weather information in a Web-based GIS environment. In addition, some data sets are being provided in a format that can be integrated into desktop GIS programs and tools have been created to convert the format and automate update processes within these programs (Liknes, Hugg, Sun, Cullen, & Reese, 2000). However, these tools do not allow for seamless integration of remote real-time databases into the desktop environment, an issue that the emergence of IMS has addressed.
Key Terms in this Chapter
SDE: Spatial Database Engine is a software product from Environmental Systems Research Institute (ESRI) that acts as a middleware between the database and applications allowing GIS data to be stored in and retrieved from a relational database, such as Oracle or DB2.
NEXRAD: Next-Generation Radar is an NWS network of about 160 Doppler weather surveillance radars (WSRs) operating nationwide.
NetCDF: Network Common Data Form is an interface for array-oriented data access and a library that provides an implementation of the interface. The NetCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data that include metadata.
Degrib: NDFD GRIB2 Decoder is the starting point for decoding the NDFD and various World Meteorological Organization (WMO) GRIB2 files. A “degribbed” file is a packed binary file or archive (GRIB2) like any other compressed archive; for more information see http://www.weather.gov/ndfd.
NDFD: The National Digital Forecast Database is a database put together by the National Weather Service (NWS) to provide forecasts of sensible weather elements (e.g., cloud cover, maximum temperature) on a seamless grid. The NDFD data sets are currently given out to the public as GRIB2 files.
Open GIS: Open GIS is the full integration of geospatial data into mainstream information technology by defining a standard syntax for requesting IMS. Particular formats include Web map services (WMSs), which are types of image services, and Web feature services (WFSs), which are types of feature services.
Image Service: An image service is a type of map service that generates a snapshot view of the spatial data requested by a client. The snapshot is stored in a standard image file, such as a JPEG, which is subsequently delivered to the client.
Map Service: A map service is a special type of Web-based service that allows spatial information, that is, maps, to be accessed remotely over the Internet and displayed and manipulated in a client software program.
Feature Service: A feature service is a type of map service that delivers raw geometry features via the Internet to clients through desktop software or applications.