Geodetic levelling networks and networks with distance measurements are analysed in order to elucidate their special features. This analysis naturally leads one to look for continuous analogons of these networks. By means of tools known from the method of finite elements we derive the corresponding Green's functions for various boundary value problems. The Green's functions act as a formal covariance function for the corresponding least squares problem and provide information on the general error behaviour in the networks. The theory is illustrated with examples relevant to the CERN survey problems.