This document discusses setting up a web-based digital city for Hong Kong. It defines a digital city as an information system that collects and monitors city data to support urban decision making. The proposed system architecture has four layers: a data layer to collect and manage city data, a technology layer to build 3D models and spatial analysis tools, an application layer to implement subsystems like transportation and tourism, and a decision layer for urban planning and management. Standards for data sharing and 3D modeling are also important considerations for developing an effective web-based digital city.

1. Department of Land Surveying and Geo-Informatics
LSGI4321 Geoinformation for Urban and Regional Studies
Individual Paper
Web-based Cybercity/Digital City is a new trend in
GIT development. Discuss and suggest the system
architecture, data standards and other relevant issues
in setting up a web-based cybercity/digital city for
Hong Kong.
1

2. Contents
Contents ......................................................................................................................... 2
Introduction ................................................................................................................... 3
Definition ....................................................................................................................... 4
Advantage of Web-based Digital City ............................................................................ 4
Limitation of Web-based Digital City ............................................................................. 5
System Architecture ....................................................................................................... 7
Data Standard .............................................................................................................. 10
Conclusion .................................................................................................................... 11
Reference ..................................................................................................................... 12
2

3. Introduction
In 1988, the former US vice president Al Gore first bought up a concept named
“Digital Earth”. The concept of Digital Earth is to represent the earth in a virtual
format, which is spatially referenced and interconnected with the world’s digital
knowledge archives.
Later, one of the concepts of “Digital City” was derived from digital earth. It
integrates different kinds of urban information and creates virtual spaces for citizens
in a particular city.
For the rises of digital city, there are lots of technologies and languages to assist for
setting up a digital city, such as VRML (Virtual Reality Modeling Language), CityGML,
AutoCAD, GIS, VR (Virtual Reality).
When the Digital City with web-based, it offers an interactive platform for integrating
and exchanging urban information, idea in an efficient way. The people can discover
more about the relationship between the environment and city development around
them.
In this paper, the general description of cybercity/digital city – the definition,
advantages of digital city using GIS are included. The system architecture and the
data standard, strength and limitations of web-based digital city are also discussed.
3

4. Definition
“Digital city is an information service system that supports city decisions by
continuous collection of city information and dynamically monitoring all possible
aspects of the city.” states Wang, L. (2001).
By using an up-to-date city model as a skeleton, with different kinds of city
information such as transportation, tourism, communication etc., are to support to
form a web-based digital city.
To make a digital city operate on the internet, it needs multi-disciplinary supports.
Different kinds of technologies, such as high-speed network, high-resolution earth
observation technology, GIS, GPS, and Virtual Reality (VR) etc can work together to
build a digital city.
Advantage of Web-based Digital City
Digital City has several advantages compared with the old format of integrating and
exchanging urban information. The advantages of Digital City can be classified into
four categories:
Easier to collect data
The digital city network with the GIS technologies makes the process of collecting,
releasing, and interoperating data in an efficient way. With the use of Internet, digital
city technologies can build up the data sharing system and technological platform for
urban sustainable development.
Effective for integration
An urban database should be built before setting up a digital city, it store the
reproduction of real city in virtual way. The database can effective integrate lots of
urban subsystems such as population, resources, transport, environment etc.
Moreover, the integrated database of digital city can allocate and utilize different
kinds of urban resources in space and time effectively. The useful decisions of urban
development can also be made with the aid of digital city.
4

5. Interactive experience
Users can have a more interactive way for discovering things of the city through
Web-based Digital City. Internet always makes the Digital City can offer a great
interactive experience for the users. Numbers of virtual modeling created a Digital
City, this offer an interactive experience for the users to explore the space and area,
and interact with the interested content as they like.
Great visualization capabilities
The models appear in the digital city are in 3D format, so 3D visualization is a key
technology that using in digital city. 3D visualization and VR enhances the efficiency
not only city planning, but also public participating. This statement is supported by
North and Macal (2007), “Visualization is one of the most effective ways to present
key model information to decision-makers.” City planners can plan the city with use
of the virtual perception. Also, the public can have the same planning experience
through web-based digital city. Since there are numbers of technologies such as CAD
technologies, CityGML, 3dmax etc., can assist the professional for 3D modeling, the
quality of the models are very high.
Limitation of Web-based Digital City
Since there are two sides to every coin, there are some limitations for nowadays
technology development of Digital City. The limitations would be listed as follows:
Underdeveloped analytical functions of 3D city models
There is a truth that analytical functionality of 3D city models is always
underdeveloped (Batty and Hudson-Smith, 2002).Furthermore, those models have
only little spatial analysis. Although the models often exist with different types of
data sets, but they are only as empty shells, there are no analysis capabilities itself.
Data gathering
Nowadays, many types of data for digital city can be achieved from different kinds of
sources , for examples, from different government departments, surveying works,
remote sensing, but some problems have been rise – how to gather and manage
large amount of data which is achieved from different sources?
5

6. An integrated multi-platform data system should be built to monitor and simulate
Low speed of generating 3D models
The speed of generating 3D models is relatively low. Also, the methods of generating
3D models are immature. Nowadays, “the development of a more automated
pipeline for 3D city modeling from satellite, aerial and terrestrial imagery and/or
LiDAR point-clouds is a challenge” states Wu (2011).
Difficult to model internal structures of buildings
Although it is easier to model the external structures of the building with the aid of
different types of technologies and resources, while, the internal structures of the
buildings are still comparatively difficult to model. The internal structures of the
buildings are very complex, such as multi-floor buildings have over several floors
with interconnecting stairways, mixed land use. It is difficult to present the complex
internal structures for the users to have an analysis inside the buildings.
6

7. System Architecture
In order to pursue the advantages of digital city that stated in the previous paragraph,
designing the system architecture is important for setting up a Digital City for Hong
Kong.
There are four layers (Figure 1) for setting up a web-based digital city– data layer,
technology layer, application layer and decision layer.
 Figure 1
7

8. Data Layer
Data collection and data management can be implemented on this layer. Firstly, a
data sharing system should be built on the server side. Different departments of the
Hong Kong government can transfer their own data of the city into this database. For
example, Census and Statistics Department can offer the population data with
different years. Transport Department can provide the transport network of Hong
Kong into this database, and the information of the traffic condition on the major
roads. Planning Department can give out the latest city planning project information
into this database.
Due to the large amount of data, spatial data clearing house and the metadata
management system are for making all data accurate and useful. Those systems can
manage the data in a correct format.
Technology layer
This layer implements the basic and abstracted functions on data layer. Technological
components such as Remote Sensing, GIS, the Internet, VR and 3D interaction are
running as important part of the integration. Though this layer, the whole Hong Kong
can be seen as 3D format. With use of Web-GIS, the users can get the spatial data of
Hong Kong in digital city. For example, the users can get the coordinates of the
particular point on Hong Kong, the distance between two sites, the area of the
particular sites.
Application layer
After the 3D models have been built in digital city, this layer can implement different
types of sub-systems on the digital platform. Each sub-system included different
functions. These sub-systems can help the professional to manage and operate the
whole city. For example, the users can view the population data in the districts unit
of Hong Kong or in building unit through 3D models. The users can get a conceptual,
virtual perception of the latest urban planning project by web-based digital city. Also,
the users can know the traffic condition of main roads in Hong Kong. The whole Hong
Kong will be presented in digital city by visualization format.
Decision Support layer
Dynamic supervision, simulation, monitoring on this layer can assist the professional
8

9. to make a decision for urban development. Moreover, this provides services to the
scientific decision and management of urban development. Also, the public can
involve in this decision layer too. The users can have a virtual urban planning on this
layer. It will visualize the possible results and outcomes of the proposed planning
decision.
9

10. Data Standard
Data types
Due to the visualization of the real whole city, large amount of data should be
involved in the system of Digital City for Hong Kong. They are, but not limited to:
Digital Terrain Models (DTM, DSM), Building Models (2D & 3D), Raster data (Aerial
Images, Textures, and Oblique View etc.), architectural models, Linder, Vegetation
models, Topology, Infrastructure, and Cadastral Data.
For higher-resolution DTM data, is used as the main part of the 3D city models.
Digital terrain model is needed to build terrain of the digital city. Building footprints,
building textures are also needed for building 3D models.
Cadastral Data is used for offering the official footprints of buildings, land parcels,
ownership and address information into the database of digital city.
For raster data such as aerial images, oblique view can be acquired by Remote
Sensing technology. Lately, the advanced remote sensing technology, and data
processing can provide a high quality of automated capturing and processing of
geodata, for example, the data of detailed building geometry - roofs, vegetation etc.
For LiDAR, the users can calculate the height statistic for each building by GIS
technology. These statistics typically include average, maximum and minimum
heights. Also, we can have the building polygon based since the LiDAR points fall
within the polygon. Building polygons can be extruded to a set height (for example
average height of LiDAR points locating within that building polygon footprint) for
visualization purposes is the result. (Batty et al, 2007)
Last but not least, topology expresses different types of spatial relationships as lists
of features. The ability to create and store topological relationships has a number of
advantages.
Geometrical elements of 3D city models
According to the geometrical elements of 3D city models, the 3D data can be
categorized by different hierarchy and complexity. (Zhu, 2009)
(1) 2D digital orthoimage map (DOM)
10

11. the texture of terrain surface, multiresolution DOMs from high resolution satellite
imagery to aerial imagery offers the details of real and provides a time stamped
record of land use, urban development and the general environment;
(2) 2.5D DEM, a digital representation of ground surface topography or terrain, is the
most common foundation of 3D city models;
(3) 2.5D linear elements, the centerlines and boundaries of road, rivers, railways and
landuse, showing the outline of an object;
(4) 3D solid objects, external and/or internal surfaces of buildings, bridges overpasses,
pipelines, stratum, etc., showing the entire volume of an object.
Conclusion
It is undoubtedly that Web-based Digital City will become a trend for the
future of GIT development. Since Web-based Digital City is a good platform for not
only visualizing the whole city in 3D format, presenting and exchanging the urban
data in an efficient way, but also assisting the urban planners for making decisions for
the future planning. This is a new trend for the professional, scientists, urban planner,
business man etc. to have a multi-angle views to discover how the environment
changes in the city, to analysis the urban information through 3D models. Moreover,
this technology offer a chance for the public to participate for the future urban
planning. Certainly, web-based Digital City will have a great impact for the future
development of a city.
For designing system architecture of the digital city, four layers – data layer,
technology layer, application layer, decision layer –should be considered in order to
optimize the interaction of the whole system. And also, the data standards are
needed to be considered before setting up a digital city.
To conclude, for the development of technology today, there are lots of strengths for
setting up digital city. Many technologies such as CAD technologies, CityGML, 3dmax,
GPU etc, can assist the technicians for building a digital city, while some limitations
still exists in the nowadays technology. In order to optimize the utilization of Digital
City, the GIT professionals need to find out the solutions to break through the
bottleneck for the 3D technologies today.
11

12. Reference
Batty, M. and Hudson-Smith, A. (2002), 'Virtuality and Cities: Definitions,
Geographies, Designs', in Fisher, P. and Unwin, D. (eds.), Virtual Reality in Geography,
Taylor & Francis, London, UK, pp. 270-291.
Batty, M, Carvalho, R., Hudson-Smith, A., Milton, R., Smith, D., Steadman, P.,
(2007), “Scaling and Allometry in the Building Geometries of Greater London”. CASA
working paper 126 (http://www.casa.ucl.ac.uk/working_papers/paper126.pdf)
North, M.J. and Macal, C.M. (2007), Managing Business Complexity: Discovering
Strategic Solutions with Agent-Based Modelling and Simulation, Oxford University
Press, New York, NY.
Wang, L., Wu, H. Y. & Song, H. (2009). A Framework of Integrating Digital City and
Eco-city. Retrieved October 18, 2011 from
http://www0.hku.hk/dupad/asiagis/fall03/Full_Paper/Wang_Lu.pdf
Wu, B. (2011). From Static to Dynamic Virtual Urban Environment: Challenges and
Considerations. ICA2011 Workshop on Persistent Problems in Geographic
Visualization, .
Zhu, Q., Hu, M. Y. & Zhang, Y. T. (2009). Research and Practice in Three-Dimensional
City Modeling. Retrieved October 18, 2011 from
http://www.springerlink.com/content/y75rg377t61r6l70/
12