Each site should be represented by a row in a Sites table, whose columns should each represent attributes which are functionally determined solely by the table's primary key. These will include locational attributes such as the longitude and latitude
of the site. The latitude and longitude should be stored either as floating point numbers in degrees, or as integers in degrees and a floating point number in minutes.
Identifying a site by its latitude and longitude co-ordinates is not a good way of going about it. Each site should be identified by a distinct primary key value, which can then be referenced by a foreign key in your sampling table(s).
As regards defining an area around a latitude/longitude point, to do so internationally would require some spherical trigonometry, but if the data is confined to a limited area an approximate square around a point can be defined quite easily by first ascertaining
the size of a minute of latitude or longitude in the area in question. In my part of the UK for instance a minute of longitude is roughly 10800 metres, and a minute of latitude is approximately 18600 metres.
Ken Sheridan, Stafford, England
