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A RASTER-BASED MAP INFORMATION MEASUREMENT FOR QOS 
Huayi Wu*, Haijun Zhu, Yi Liu 
State Key Lab of Information Engineering in Surveying, Mapping and Remote Sensing 
Wuhan University, Luoyu Road 129, Wuhan, China, 430079 
Email: wuhuayi(mail.liesmars.wtusm.edu.cn 
Commission IL, WG VI/6 
KEY WORDS: Internet/Web, GIS, Information Measurement, Mapping, Visualization, Services 
ABSTRACT: 
With the changing status of GIS from desktop to distributed environment, geographic information is more often required to transmit 
over networks. As geospatial data is in essence of huge volume and complicated but the bandwidth of a network is limited, it is of 
great importance for map-QoS to transfer data as less as possible. This paper discusses this problem from the view of information 
theory and proposes a novel approach of information measurement for minimizing of geospatial data size while delivering map 
information constantly. 
This paper starts from a discussion of map-QoS concerning map as a media carrying geographic information. Either on various 
display mechanisms or on paper-alike media, geographic information is transformed to map, an image to stimulate visual sentience 
of human being. However, visual sentience of human being has only limited spatial and frequency resolutions. Map with resolution 
approaching or higher than this limit increases little or even decreases the amount of information contained. Display mechanisms 
and paper-alike media also have their maximum spatial and frequency resolutions. It is impossible for a map to display more data 
than its capacity. For map-QoS, the size of geospatial needed is the minimum to reach this capacity. 
Based upon above understanding, this paper proposed a raster-based measurement of geographic information contained in a map. A 
study of the relationship between data size and map information by this measurement reveals that this is usually a mono-modal curve 
with a single peak. 
approach in this paper to minimize geospatial data size while 
delivering sufficient map information in a smooth manner. 
1. INTRODUCTION 
Web-Based Applications have gained predominant advantages 
over other ways of information dissemination during the past This paper discusses map-QoS concerning map as a media 
few decades, and with the changing status of GIS from desktop carrying geographical information. Either on various display 
to distributed computing environment, geographic information mechanisms or on paper-alike media, geographic information is 
is more often required to transmit over networks. Yet, transformed to map, an image to stimulate visual sentience of 
information interchanged nowadays on the WWW is mostly in human being. However, visual sentience of human being has 
the forms of hypertexts, highly compressed images (such as ^ only limited spatial and frequency resolutions. Map - with 
GIF and JPEG), and short movie clips that are small in size. resolution approaching or higher than this limit increases little 
Large Objects, such as audio and video can only be transmitted or even decreases the amount of information contained. Display 
via a special suite of protocols and must rely on broader mechanisms and paper-alike media also have their maximum 
bandwidth due to their big size, so it is not very popular. This spatial and frequency resolutions. It is impossible for a map to 
situation will not change in the near future and unfortunately is display more data than its capacity. For map-Qos, the size of 
what the Web-based spatial information service is faced with. geospatial data needed is the minimum to reach this capacity. It 
While the demand for spatial information through a limited is based on this consideration that our new approach is 
bandwidth (i.e. a 56.6 kbps modem) is emerging and geospatial proposed. 
data is in essence of huge volume and complicated, it is of great 
importance to transfer map data with acceptable QoS (Quality The remaining part of this paper is organized as follows. 
of Service) which makes users get what they expect within a Section 2 gives a brief introduction and an overall evaluation of 
relatively small delay, even when they connect to Internet via a current methods of map information measure; Section 3 discuss 
limited bandwidth. But situations in the spatial information our approach of raster-based map information measurement 
service arc not satisfactory. When a user sends a request for an concerning relations between data and information; Section 4 is 
geo-information concerned service, both the user and the server an experimental research and some conclusions are drawn in 
cannot know in advance how much bytes of data must and will Section 5. 
be transferred over the network, there is no way to determine 
the most suitable data amount that must be transferred which 
not only can fulfil the demand of variable kind of user but also 2. A BRIEF DESCRIPTION OF AVAILABLE 
is the minimum data amount that is needed. To meet this METHODS OF MAP INFORMATION MEASUREMENT 
dilemma, some principles must be utilized to direct the 
eospatial data. We present a raster-based Quantitative measure of information had appeared when 
Shannon (1948) put forward his famous information theory in a 
transmission of 
y 
e 
365