The underground geothermal conditions can be presented, irrespective of the aquifers' position, with the appropriate geothermal maps. It is made on the basis of measured temperatures in accessible boreholes throughout the country. However, since the temperature field depends on the geological structure in the depths and tectonic characteristics, the course of the isotherms is a result of many influences, such as thermal conductivity of rocks, permeability and fracturing of rocks, all of which are reflected in the measured temperatures in boreholes. The distribution of boreholes, which were useful for the measurement of temperature, is very uneven and different as regard the depths. In the northeastern part of the country the anomaly is the result of the thinning of the Earth's crust and greater conductive heat flow from the Earth's mantle.
COMMISSION REGULATION (EC) No 976/2009 of 19 October 2009 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards the Network Services