Each cost estimate is calculated using either country specific parameters or appropriately modified parameters from other countries with available data (i.e., by extrapolation). For example, as regards estimating the operating costs of the border crossing points, only one (Finland) out of the 12 Schengen countries with external land borders provides a publicly available detailed breakdown of border maintenance costs. Yet, Finland is an exceptional case, as the Finnish-Russian border goes through mostly uninhabited territory with a high degree of natural vegetation and low number of permanent border crossing points. Thus, it was deemed inappropriate to use the Finnish data as a basis for cost extrapolation to other countries other than Sweden and Norway, which have borders very similar to the Finnish-Russian ones. To circumvent the issue, data from Switzerland and Latvia were used. However, both these countries provide data for the overall expenses related to border protection only, thus preventing a detailed analysis. The data were used as a basis for extrapolation to other countries by using the number of border crossing points as the common denominator.