Senior Land Surveyor (Mapping Information Services)
Survey and Mapping Office, lands department, hong kong
A multitude of possible usages of digital maps has reached down to an enormous users’ base in Hong Kong with the growing popularity of the Internet. The entire region has been covered in the large-scale topographic maps, which have all the basic GIS elements built in
Traditional maps on hardcopy form are fragile, difficult to handle, bulky and require enormous storage space. Updating the paper maps requires partial or complete redrawing of a large number of repromats that is time consuming, labour intensive and costly.
It was not until the 1990s, with the advent of GIS technology, that map information had a complete face-lift, and entered into a new era. It is no longer bound by the map production scale and physical size of paper, that is, display and printing of maps can be at a variety of scales based on one map base. The map features can be updated one by one as they are changed, and input into the database for instant use. The various map features are topologically structured and relevant textual attributes can be attached to them, thereby enabling the selective search for required features and supporting polygon overlay analysis of map features and attached attributes. Digital maps provide versatility in storage and dissemination methods.
Hong Kong Situation
Hong Kong has a land area of just over 1,100 sq km, but with a high population of 6.8 million. Most people live in the urban areas around the harbour and in the new towns. Maps have been relied upon as the basic essential information for the administration of and use by the community. In Hong Kong, the maps are produced and maintained by the Survey and Mapping Office (SMO) of the Lands Department, the Government of the Hong Kong Special Administrative Region. The large-scale topographic map at scale 1:1,000 and with a total number of some 3,000 sheets covering the whole region had been converted from hard copy into digital form in mid 90s. While designing the digital map base very stringent specifications had been laid down, on one hand to fully exploit the GIS functionalities and on the other to create a geographical database that would facilitate the building up progressively of a comprehensive geographical database for Hong Kong.
The topographic maps show almost all noticeable natural and artificial features on the ground, e.g. roads, footpaths, buildings, temporary structures, lamp posts, fire hydrants, cuttings and slopes, trees, contours lines at 2 metres interval etc. All these features are captured and input to an accuracy of better than quarter of a metre, and all types of features are separately coded and layered in the database. They are also topologically structured, such as: buildings and land parcels are closed polygons, road lines and contour lines are continuous and with respective names and values. Attributes are attached to the map features thereby enabling the searching for and analysis of relevant features and attributes for answering various ‘what if’ questions. Several commonly used location identifiers are also built in too, such as: house number, building name, road name and junction, land parcel number.
More importantly, the map base is updated instantly as changes take place. Unlike the paper maps which are revised on a cyclic programme, normally a couple of years, while substantial changes have been accumulated, but with the digital map base, change to any individual feature no matter big or small, e.g. a new road or a new lamp post, can be input into the database soon after having been surveyed in the field and ready for use instantly. In the case of Hong Kong, the target is to update any map features, namely to delete the old features and input the new ones, within three months of such changes. That is particularly important in order to maintain the currency and reliability of the digital maps, which are widely used within the government and in the private sector.
By now, a wide range of smaller scale topographic maps and thematic maps are being compiled and published from this basic map base. Many government departments and private utility companies are relying on this map information for their respective operations and even using this as a reference base to record their own facilities information, such as: cable, drain, pipe, town planning layout etc. Indeed, the digital maps of the SMO are serving many useful applications and gaining high regard as being accurate, up-to-date and comprehensive. It is also realized that the potential of these digital maps is tremendous and effort is being made to explore new applications.