The migration statistics represent a more complex field than it appears at first sight. Difficulties already begin at the attempt to define “Homo Migrans”. What constitutes migration? Can a move from one neighborhood to another be put in the same category as the classic overseas migration of the 19th century, which occurred via wagon trains, railroads, river boats, sailing ships, and ocean steamers, and often included foot travel over huge distances? Is it legitimate to allocate a temporary change of residence to the same category as long term and permanent moves? Can seasonal migrations into neighboring countries be assigned to the category of emigrations without further analysis? To what extent are commuters migrants? Should a phased migration, such as the one of the Klettgau hamlet of Osterfingen through the cities of Schaffhausen, Zurich, and New York to Curtis in the U. S. state of Nebraska, be seen as a migration type sui generis, or should it be interpreted as a demographic movement consisting of multiple migration processes? Migration historians familiar with the idiosyncrasies of highly aggregate statistics are constantly confronted with such problems that can usually only be solved by making arbitrary definition assignments. Officials who were charged with the sorting and classification of primary data material received by the government faced similar if not the same tasks at their time. Anyone using data from the following tables should be aware of this fact.

Since there are no annual cantonal statistics for emigration and internal migration before the early 1980’s, we did not present those series. Instead, we considered part of city migration and naturalization statistics the recording of which began much earlier. Documentation available on the development of the city of Zurich and the canton Basle-City is the most accurate and goes back farthest. This caused us to substantially limit our presentation of migration and naturalization in larger cities to Zurich and Basle. It should be mentioned, though, that the Statistical Yearbooks of the cities of Berne, St. Gall, and Geneva contain such data as well.

The statistical picture of Swiss overseas emigration in the period of 1816–1939 is the subject of the dissertation of H. Ritzmann-Blickenstorfer. Since that study contains detailed information about the origin, depth, and quality of the data, there is no need to describe those sources again here. Similarly, there is no need for additional commentary to the estimates performed by Ritzmann-Blickenstorfer.

With regard to the statistics of Swiss living abroad, it must be noted that the periods 1850–1910, 1926–1950, and 1951–1992 are comparable only conditionally. The massive decrease of Swiss living in the United States between 1910 and 1926, for example, is mainly explained by the fact that the 1910 U. S. census included all Swiss-born individuals while the 1926 census is largely based on a tally of Swiss nationals matriculated at consulates and embassies. In general, it should be assumed that any counts of the pre-war era yield approximate values at best.
When interpreting comparative naturalization figures, it must be considered that Swiss naturalization practices differ substantially from those of other countries, and that even within Switzerland naturalization conditions vary widely from community to community.