ABSTRACT:Many organizations and groups are active in the field of standardisation. The "official" standards are published by the International Organization for Standardisation (ISO). Through the work of its Technical Committee 211 (ISO/TC 211) the ISO has taken the leading position in the standardisation of geographic information. The ISO/TC 211 has created a complete suite of standards for vector-based GIS which integrates all major developments in this field.The ISO-numbers for the geographic information standards are between 19101 and 19199 presently ending with 19140. The reference model, the spatial and temporal schema, the referencing by coordinates, the portrayal, the encoding and the metadata are typical titles of the individual standards. These standards have been completed in Phase 1 since 1994. Phase 2 focuses on imagery, gridded data and coverages. Those standards will be the most important development of the ISO/TC 211 in the coming years.Typical standardisation projects of Phase 2 are the reference model for imagery, the sensor and data model for imagery and gridded data, the encoding for imagery, and the metadata for imagery. The sensor and data models contain a comprehensive approach towards the classical and the new sensors of photogrammetry and remote sensing such as the photogrammetric camera, line sensors, and film scanners.Most of the ISO 19100 standards contain abstract solutions. Standards on the implementation level have been defined by other organizations such as the Open GISConsortium. In many cases the implemented solutions are well established existing formats or environments. However, many recent implementation developments are strongly influenced by the ISO works including the use of the Extensible Markup Language (XML), web-based services, and location-based services.
SUMMARY The rheological properties of the lithosphere in the East African Rift System are estimated from regional heat flow and seismic constraints. Heat flow data are used to infer average, maximum, and minimum geotherms for the Eastern Rift, the Western Rift, and the surrounding shield (having surface heat flow of 106±51, 68±47, and 53±19mWm−2, respectively). Combining the geotherms with brittle and ductile deformation laws for a lithosphere of appropriate structure and composition yields rheological profiles, thickness of brittle layers, and thickness and total strength of the lithosphere. The thickness of the uppermost brittle layer varies from 10 ± 2 km in the Eastern Rift, to 186‐9km in the Western Rift, and 26+ km in the shield; seismicity is confined to the brittle layers. The rheological thickness of the lithosphere in Eastern Rift (23+8‐9km), Western Rift, and shield is approximately in the the ratio 1:2.5:5, and matches the elastic flexural thickness. The total resistance to deformation is one order of magnitude larger in the shield than in the rifted regions (˜1012N m−1), where the whole lithosphere is probably in a state of failure.
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A 57,000 line kilometer, high‐resolution aeromagnetic survey was flown in 1987 as a contribution to the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE). Existing aeromagnetic data from the United States and Canada were combined with the new data to produce a composite map and gridded data base of the Lake Superior region (Figure 1). Analysis of the new data permits more accurate definition of faults and contacts within the Midcontinent Rift system (MCR). The aeromagnetic map provides important information supplemental to the seismic profiles acquired under the GLIMPCE program in 1986, allowing lateral extension of the seismic interpretation. In particular, modeling of the data provides an independent assessment of a reflection seismic model derived along line A (Figure 2). The profile and gridded digital data are available to geoscientists through the Geophysical Data Centre of the Geological Survey of Canada (GSC), while the gridded data are available from the USGS‐EROS Data Center. GLIMPCE was established in 1985 to study the nature and genesis of the crust in the Great Lakes region. Program participants include the GSC, the U.S. Geological Survey (USGS), provincial and state surveys, and Canadian and American universities. In the Lake Superior area, a major objective of the program is to develop thermal, tectonic, and petrogenetic models for the evolution of the MCR and to evaluate these in the broader context of the tectonic evolution of the North American continent. Pre‐1982 geological and geophysical knowledge of the MCR in the Lake Superior region has been summarized by Wold and Hinze [1982]. The Lake Superior region provides a unique window on this Proterozoic rift system, exposing igneous rock of the Keweenawan Supergroup that disappears under Paleozoic cover to the southwest.
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