Firstly, the physical reference for vertical information in the two datasets is 
fundamentally different. Land based data is referenced above a vertical 
reference point (normally determined by tide gauge data from several points). 
Bathymetric information, while tied to the same points is referenced to a 
local datum and the absolute value changes with the effect of water level 
fluctuations . Horizontal reference surfaces are essentially the same, although 
the precision with which horizontal position is determined is often higher 
for land based data than for water based data. 
Time is a very important element of much of the data collected at sea - such 
things as water temperatures, salinity, fish landings, chemical concentrations 
etc. vary with time of year, time of day, and vertically within a column of 
water. Although time may be a factor in some land based data, it generally 
does not play as prominent a role. 
The techniques available for data collection are different for collecting land 
based data as compared with water based data. It is easy to "see" the objects 
you want to map on the land - this makes aerial photography, GPS 
positioning, remote sensing from satellites, and traditional ground surveys 
appropriate methods for collecting this data. It has not been as easy to "see" 
what is under the water's surface. Recent advances in swath and sweep 
techniques have made it easier to "see" the sea bottom, but most bathymetric 
data available today is still of the sounding profiles variety, and most water 
based thematic data is still being collected as points, leaving large areas of 
uncertainty filled with interpreted estimates. 
The water based data community has concentrated recent research dollars in 
two main areas. One is to devise a database engine, with facility for handling 
spatial temporal information and even multi dimensional information that 
could be used in a distributed environment. The other is to coordinate the 
collection and management of water-based data from all sources. 
Management of information is clearly a priority with the water based 
custodians. In general, recent efforts managing the land based data has been 
more in the applications area - devising new ways to use the data already 
collected to produce a new service for a customer. 
Developing a coastal dataset - one which merges data taken from these two 
worlds - thus poses some challenges. Standards are important. At the very 
least standards dealing with reference systems, data models, access to 
information etc. must be pursued. Cooperation among the different players 
is equally important. The effort required should not be underestimated - 
much of the entire water based community and much of the land based 
community must be involved. There has been significant progress in 
achieving cooperation between the feds (CHS) and the provinces (NS and 
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