Introduction
Geo-related data are of national fundamental datasets that are used in different applications particularly development plans. In Iran, GSI is in charge of producing these kinds of data and during the last decade GSI has been able to produce a large amount of geo-related datasets such as geological, geotectonic, geophysical and geochemical maps. However, potential users have different problems for using these datasets in their projects. The most important problems can be summarized as:

• Users are not aware of available data in GSI. In other word, GSI has not an appropriate mechanism for awaking potential users of available datasets in GSI,
• GSI does not have a clear policy and mechanism for access of users to geo-related datasets,
• Geo-related data have not been producing based on a clear standard. Each map sheet has its own standards and specifications. Such a situation makes it difficult for users to seamless datasets, integrate data with each other and in general using data in their projects, and
• Available data, particularly geological and geochemical maps, are not well-prepared and well-structured for direct use in Geo-spatial Information System (GIS). This situation is also problematic for users during utilizing geo-related datasets.

• To ignore using geo-related data in their projects that causes inadequate decision-making and planning, or
• To reproducing their required data or to spend some time for editing, structuring and making them GIS-ready. As such activities cost a lot and require employing new Spatial Information technologies, so this situation is not cost-effective particularly from a national point of view.

• Recognition: organizational assessment and need analysis with an spatial data point of view,
• Data standardization,
• Metadata standardization,
• Data and metadata preparation based on developed standards,
• Design and development of a clearinghouse service, and
• Integration of data and the developed system.

Recognition
At the first step of the project, GSI was assessed with respect to spatial data. Available data in GSI and their specifications as well as policies of GSI for offering these data to users were investigated. The investigation highlighted that a plenty amount of datasets have been producing by GSI or exists in this organization. The most important ones can be named as:

• 1:1M scale geological map of Iran,
• 1:250K scale geological maps of Iran,
• 1:100K scale geological maps of some parts of Iran,
• 1:100K geochemical maps of some parts of Iran,
• 1:1M geophysical maps of Iran,
• 1:100K geo-structure map of some parts of Iran,
• 1:100K scale mineral potential maps,
• different satellite imageries such as Landsat ETM+, Radarsat, Spot and IRS-1C, and
• 1:250K scale Digital Elevation Model (DEM) of Iran,

Data Standardization
At the second step of the project, unique standards were developed for available data in GSI. All three sources of heterogeneity including semantic, syntactic and schematic heterogeneities (Zaslavsky et al., 2000 and Moustafa, 2000) were considered during data standardization. In the context of semantic standardization, definition, primitives, structure and coordinate system of data layers were clarified. With respect to semantic standardization, data format and DataBase Management System (DBMS) were clarified. Regarding schematic standardization, data model, data coding and topology were clarified. Further works on standardization is still required in order to reach all aspects of an interoperable system, for at least, in Iran.

Metadata Standardization
Metadata which is data about available datasets is the main component of a clearinghouse service. In this regard, at the third step of the project, metadata standards were developed for GSI's datasets by adopting ISO TC/211.

Data and Metadata Preparation
At this stage, for a 150 x 300 km2 area in east of Iran, available datasets were prepared based on developed standards. Metadata related to prepared datasets were also generated based on metadata standards.

Design and Development of a Clearinghouse Service
A Clearinghouse is a server or decentralized system of servers on the Internet, which contain field-level descriptions of available spatial data (metadata) (adopted from Nebert, 2001). Metadata are collected and served in a standard format to facilitate consistent queries and data-presentation across multiple participating sites (Molina, 2003). A fundamental goal of a clearinghouse is to provide access to digital spatial data through metadata. From user's perspective, the clearinghouse is a service to discover which organization has which data and its fitness to use (Molina, 2003).

From the database management perspective, there are generally three approaches to store and manage spatial data including centralized, distributed and hybrid data storage/management system. With this in mind, three architectures can be considered for clearinghouse services with respect to metadata storage/management system namely centralized, distributed or hybrid architecture.

From spatial data display and analysis point of view, three levels can be considered for clearinghouse services:

• level 1: user can search its required data and then access the desired data if available,
• level 2: user can search its required data. If the data were available, it is possible to display the data for further checks or evaluations. There are also tools or services for accessing data or ordering them, and
• level 3: user can search its required data. If the data were not available, there are services for data processing and analysis to generate required data from available sources.

Integration of Data and the Developed System
At this stage, prepared data and metadata in the previous stages were integrated with the developed system. The system has been installed in GSI and is operating based on available Local Area Network (LAN) in GSI. The system is currently under test and evaluation.

GSI is also involving in preparing its other data and related metadata based on developed standards. The service is going to be launched on internet after finalizing its tests.

Conclusion
In this project a clearinghouse service for awaking users of available geo-related data in GSI was developed. Appropriate standards for geo-related data and their metadata were developed as well. These standards facilitate direct use of geo-related data in GIS environment. The standards also facilitate integration of geo-related data with each other and with other datasets (such as topographic maps) in different applications.

By means of the developed clearinghouse service, after connecting to internet, users can search their required data, retrieve data specifications and also display data for further check and evaluation. By finding appropriate datasets, users can order data or arrange to get them from GSI. Meanwhile, GSI should clarify its policies for offering its data to users. Otherwise, the clearinghouse service will have just the role of awaking users of available data and accessibility of users to geo-related data will have sill problem due to ambiguity in the accessing and offering processes/regulations.

The GSI's clearinghouse service will be later linked to national spatial data clearinghouse and also will be more developed based on National Spatial Data Infrastructure (NSDI) requirements. For developing the national spatial data clearinghouse and for linking GSI's system to the national clearinghouse, it is necessary to use ontology concepts in order to increase the performance and usability of the systems.

References

• Molina, X. (2003). Conceptual Design of the Ecuadorian Geospatial Data Clearinghouse, an MSc Thesis, International Institute for Geo-Information Science and Earth Observation, Enschede, The Netherlands, March 2003.
• Moustafa, M. M. (2000). Geographical Information Infrastructure (GII) to support decision-making in urban development in Egypt, an M.Sc. Thesis, The International Institute for Aerospace Survey and Earth Sciences, Department of Urban Planning and Management, ITC, Enschede, The Netherlands.
• Nebert, D. 2001. Discovery Services for Geospatial Data. http://www.fgdc.gov/clearinghouse/sdi/nebert2.ppt. accessed on January 2003
• Zaslavsky, I., Marciano, R., Gupta, A. and Baru, C. (2000). XML-based spatial data mediations infrastructure for global interoperability, 4th GSDI Conference, 13-15 March 2000, Cape town, South Africa.