Anyone browsing the OSGeo software lists will find a number of catalog and infrastructure applications. They look to be mature and active projects, but they simply fail to grab the attention that applications like GeoServer and OpenLayers do. What are these applications, and why are there a number of applications that appear to do very similar things?  This article attempts to clear things up and dives into such applications as MapBender, GeoNetwork OpenSource, and deegree; as well as take a look at Spatial Data Infrastructures.

Spatial Data Infrastructures

Although many of these systems are intended to manage multiple geospatial data sources from different sites; they are all designed to work with a Spatial Data Infrastructure (SDI). So what is an 'SDI'?

A Spatial Data Infrastructure (SDI) is a framework of spatial data and associated metadata. The framework also includes the policies, standards, and people who use the framework. This includes software tools that are interactively connected to use the data efficiently and in a flexible manner. A definition used by the US White House is "the technology, policies, standards, human resources, and related activities necessary to acquire, process, distribute, use, maintain, and preserve spatial data" ( http://www.whitehouse.gov/omb/circulars/a016/print/a016_rev.html ).

Such SDI frameworks are typically built around the principle of decentralization. Data and metadata are managed by the data's originator and/or owner, and not a central organization. Therefore the software tools, standards, and policies mentioned above are an important part of an effective SDI.

Due to their size, SDIs are usually goverment run or government related. Many government SDIs also include (or are open to) private, non-profit, and academic partners. Often the driving force for a government-run SDI is that it can help manage and share geospatial data in an environment where many different organizations collect and manage very similar or even overlapping data. Ie. it helps to reduce the "silo" effect of government departments. As such they are usually promoted as reducing costs by reducing duplicate effort.

There are currently a number of government SDIs in existence or being built. Examples include:

• Canadian Geospatial Data Infrastructure
• European 'INSPIRE' Initiative
• USA's National Spatial Data Infrastructure (NSD)
• United Nations Spatial Data Infrastructure (UNSDI)

deegree

deegree (http://www.deegree.com) is a Java framework intended to provide the building blocks for an SDI whilst implementing various Open Geospatial Consortium (OGC) and ISO standards. It is published under the GNU Lesser GPL open source license. It consists of the following components:

• deegree Web Services: Includes WMS, WFS, WCS, gazeteer, WPS, security services, and owsWatch service monitoring
• deegree iGeoPortal: A modular portal framework that supports maps, a gazeteer, catalogs, security, data, and 3D
• deegree iGeoSecurity: Security framework
• deegree iGeo3D: Store & visualize 3d geospatial data
• deegree iGeoDesktop: Desktop GIS for accessing the SDI

As would be expected, deegree supports a wide range of vector and raster encodings, including ESRI shapefile, MapInfo MIF, GML, KML, GeoTIFF, PNG, and ECW.

MapBender

MapBender (http://www.mapbender.org) describes itself as "...the tip of the iceberg, a meta layer of software providing access to the OSGeo SDI stack". In other words, it is intended as an easy to use, highly focused web application for accessing an SDI. A typical MapBender application has only the required functionality for the application at hand. This simplifies the user interface, making it easier for a general user with limited GIS training to use.

MapBender provides a data model and interfaces allowing OGC-compliant map services to be displayed, navigated, and queried. MapBender also includes authentication & authorization services, and management interfaces for user/group/service administration.

MapBender is based on PHP, JavaScript, and XML; and is licensed under the GNU GPL open source license. MapBender is also modular, and encourages developers to create their own modules to access new kinds of data.

GeoNetwork Open Source

GeoNetwork Open Source (http://geonetwork-opensource.org) describes itself as a "standards based Geographic Data and Information Management System for the web". It is essentially a catalog application designed to manage spatially referenced data, and includes metadata editing facilities, search functions, and an embedded interactive web map viewer.

The management facilities include the ability to upload or download all supported kids of data and documents. It also supports distributed catalogs through the scheduling of metadata harvesting and synchonization. As with MapBender and deegree, access control is fine-grained with both group and user management abilities. All these features combine together to form what the project calls the 'glue' that binds the components of an SDI together.

As with the above applications, GeoNetwork Open Source, is open source and meets a number of OGC and ISO standards.

Conclusions

Although most geo-web developers do not work with the type of large distributed systems that make up a Spatial Data Infrastructure, it is useful to know that there are a number of mature, open source applications that can be used to leverage this ability if required. Open source geospatial web applications and servers do not have to be small scale applications, but can be (or be a part of) a large national or international infrastructure.