Aerial photograph interpretation (API) is an essential component of a geotechnical desk study. It provides an understanding of the geomorphological setting and the development of a site over time as well as information on, for example, past landsliding and site formation works. API is particularly useful in Hong Kong where thick vegetation now obscures hillsides and may hide critical features. An examination of historical aerial photographs, taken when the vegetation cover was more sparse, may be the only means of detecting such features.

The Planning Department of the HKSAR Government produces a wide range of planning documents, including Outline Zoning Plans, Outline Development Plans, Layout Plans, site search proposals for facilities of strategic importance and reports on regional planning studies. These documents are circulated widely within government for comment, including the GEO. The Planning Division is responsible for reviewing the documents, seeking views from other Divisions within the CEDD and preparing a consolidated response. GEO's contribution to the planning process is aimed at ensuring that geotechnical issues are properly addressed at the early planning stage, especially with respect to slope safety.

The Planning Division provides a geological consultative service to all Government departments, the private sector and the general public. The service includes advice on engineering geological aspects of land use planning and development in Hong Kong, particularly where such aspects may pose a significant constraint on project feasibility or public safety. Use is made of the archival geological maps and field sheets, rock thin sections, mineral and fossil collections, ground and aerial photographs, and old mining records. Other resources include a computerised bibliography of Hong Kong geology and a limited library.

The Division maintains a comprehensive rock and mineral reference collection, which include a large number of thin sections and bulk rock samples. Samples have been collected from all over Hong Kong and are available for inspection on request. A small collection of representative fossils has also been established. The Division operates a small laboratory equipped with rock cutting and grinding equipment, and two polarising and stereo microscopes.

The Geological Modelling System (GMS) is a Geographic Information System (GIS) for storage, integration, interpretation and presentation of Hong Kong-wide geological, geophysical and geotechnical data. Each of the data sets contributes to our knowledge and understanding of the rock and soil materials that underlie Hong Kong, the distribution of the materials, and the processes involved in their development. The system enables access to raw data, and current interpretations of data. New thematic maps can be generated from the data, i.e., by user-specified combinations of datasets and plotted at a range of scales. Non-database information and cartography is added using the CAD-system in the Division's Cartographic Unit (linked by network to the GMS). More sophisticated queries or analyses generate output that can portray geological or terrain models, factors that may influence planning zonation, geological hazard assessments and environmental conditions.

Data

The GMS holds four main categories of data:

1. Planning Division regional surveys including: geology, geotechnical area studies, natural terrain landslide inventory, regional gravity and stream sediment geochemistry. These datasets have Hong Kong-wide coverage.
2. Ground Investigation data (e.g. drillhole data, seismic profiles, magnetic field data). The Planning Division attempts to get Hong Kong-wide coverage, but development is shared with data-owners or other users.
3. Project or site-specific data collected by Planning Division, usually for limited areas. Examples include mapping for forensic landslide studies, specific infrastructure development or other project related data.
4. External datasets, for example: Lands Department base maps, satellite images, aerial photographs, and orthophotos etc).

Data usage

The data is mainly used within Planning Division for a variety of projects, for example:

• Stream sediment geochemical atlas
• Natural Terrain Landslide Studies
• Landslide studies
• Complex geology at Tung Chung
• Aerial photograph interpretation

Data availability

Planning Division's data is available to other users with permission of the Chief Geotechnical Engineer/Planning (though special conditions and restrictions apply). Users include other divisions in Civil Engineering and Development Department, other Government Departments, Government Corporations, Developers, Consultants, and Universities.