By simply clicking a button, the administrator makes the 
data supplied publicly available and an integral part of the 
system, without differences with those already present. 
The same is true for the suggested measurement stations 
that can directly enter the suitable layer of the map. 
The administrator also decides the graphical and 
informative features of the map that will be displayed to 
the users. For instance, he can decide which layers 
should appear and with which color or texture. This is not 
a purely graphical problem, since the existence of a 
certain layer implies the possibility of finding the 
geographical entities belonging to it. 
In a certain sense, the administrator plays the role of 
“moderator” in a standard news list. He guarantees that 
the material available in the system satisfies certain 
minimum informative constraints so that the system can 
grow with the contribution of the users, but maintains the 
desired standard. 
5. IMPLEMENTATION 
From a technical point of view, the system is based on the 
use of MapObject, a library of software components for 
map management and display (ESRI, 1996) and the 
related Internet Map Server (IMS), for the use of 
geographical representations over the Internet. The 
interfaces for both the user and the administrator are built 
in Visual Basic and utilize the Active Server Page (ASP) 
technology. An alternative approach would have been the 
use of Java as proposed by Kazakos et al. (1998). The 
DBMS that stores metadata information is Access. This 
choice is due to the limited capabilities required to the 
DBMS: since it simply stores metadata information, the 
number of records to manage is in the order of few 
thousands. On the contrary, data themselves are stored 
on the server disks in their original (or compressed) 
format. Since they are managed by the standard file 
system, they may reach several Gigabytes of information, 
without constituting a problem. 
Filling an alphanumeric form of the user interface, a query 
to the database on the server is generated. The results of 
such a query are again formatted in HTML and sent back 
to the user. The situation is exactly similar for 
geographical queries. They are passed to MapObject 
through IMS and MapObject formats their result as HTML 
pages, again sent back to the user. 
The overall work of the system relies on the Microsoft 
Internet Information Server for the Windows NT based 
computer that hosts the web site. 
The last software component is AspUpload, a .dll 
extension to ASP capabilities that resides on the server. It 
allows to separate files coming from a client browser and 
store them on the local disk. 
All internal data of the system are stored in terms of tables 
so that the administrator can easily modify them. For 
instance, a table contains the information about the entity 
types (map layers) with the indication if they are polygons, 
lines or point and the attributes for displaying (yes or no, 
order, color, style). Additions to this table, as already 
mentioned, are possible, but would imply a revision of the 
automatic mechanism that defines the relations between 
entities. However, the administrator can easily change the 
order or the graphic appearance of the different layers to 
modify how the users see the map. When a client browser 
requires a geographical operation, this table is read for 
producing the map and the related legend, in the form that 
the administrator has decided. It is evident that all the 
users connected to the server have the same graphical 
representation and cannot modify the characteristics of 
the map. 
ASP Page 
Fig. 6 - Use of an Acces table to build the ASP of data 
categories 
As another, very simple example, figure 6 shows how the 
Access table containing the name of the possible data 
categories is transformed into an ASP page for displaying 
on the user browser. Clearly, the browser itself must be 
compatible with this technology. 
The present implementation stores around 500 data sets 
in the area of Lombardy region in Northern Italy. 
6. SEARCH AND RETRIEVAL EXAMPLE 
When a user enters the site, first he has to choose the 
type of activity: search or data submission, and then the 
way to perform such a search. Even in case of data 
submission, first the user has to select a certain entity to 
which the data should be associated, except if he or she 
intends to suggest the creation of a new station. 
Fig. 7 shows an example of search based on 
geographical entity and time interval of interest (e.g., data 
on Lake Lugano after April 1995). 
i\ V* •*<}:<<' (■ . f '< 1*1« 
O INVERIGO ™ 21 
M O La Valascia (Torrente) 
||8 0 LAGLIO 
\ O Lago di Alserio l| 
O Lago di Mezzola .. 
';; O Lago di Montorfano '<4& 
I : O Lago di Piano 
O Lago di Pusiano Up 
|p O Lago di Seqnno 
O LAINO ^ ||i 
£mh> sefo/ioMtr, 
::isj Laao diLuciano m 
Fig. 7 - Data search based on time and entity name 
criteria