What data of the available Bührer dataset actually made it on one of the maps? A mosaic plot, done with the vcd package from the open source statistical software R (https://www.r-project.org), gives a quick overview over the relevant factors.
The plot essentially shows areas proportional to the number of persons, ordered by the emigration status (left) and map # (top). For a given combination the successive blocks in the color red, black and grey denote Named, Married and Descendants persons respectively (see The methodology – preparing genealogical data for maps for explanations). These three categories make up roughly 4’500 persons of the original dataset, with the remainder not being shown. The small circles denote combinations that didn’t occur in the dataset.
A few observations:
Only a small fraction of persons in the dataset actually show up on map 1 and 2. This is comes as no surprise, given the large number of e.g. Swiss-based Bührers, “Assumed US” persons as known descendants of emigrants with no place information or “Undetermined” persons where location information could neither be determined nor inferred.
The number of Bührers emigrating for the generation prior 1880 (map 1) is significantly larger than the number of emigrating spouses from Switzerland, reflecting the fact that most married once overseas. A look at the category “Third country emigrated to US” indicates that a substantial part of the Bührers – at least for the first generation – preferred to marry other emigrants.
There’s very little Bührer emigration happening for the generations born after 1880 (map 2) – almost all Bührers in that period are America-born.
Data for the emigration map project was – except for the genealogical data – all from public sources. Interestingly enough there is also a relative wealth of sources with relevant historical GIS data.
Genealogical data from Swiss Buehrer Web Site as of October 2011 (http://www.myheritage.de/site-72226521/swiss-buehrer). For practical reasons (notably less work for georeferencing) all persons not linked to the main family tree were removed as well as substantial irrelevant side lines like the Finney emigration from Ireland.
Digital Elevation Model DEM (30” resolution) from U.S. Geological Survey (ftp://firstname.lastname@example.org/data/gtopo30/global/) provided the base for the fairly easy looking smoothed hillshade layer that proved to be the most difficult to produce.
The four 30” DEM tiles delimited by longitude/latitude (W140N90, W140N40, W100N90 and W100N40) that cover the United States were merged into a single DEM file which was subsequently reprojected and downsampled, all in QGIS.
In GRASS a moving average was applied to the DEM which was exported as a GeoTIFF. From there, gdaldem was used to generate a hillshade GeoTIFF that received final blurring in Photoshop. Anything but easy.
Historical US census data (1870) from the National Historical Geographic Information System NHGIS of the Minnesota Population Center (https://data2.nhgis.org/downloads). The custom download data included e.g. the number of Swiss-born citizens per county and other interesting data that was not yet used in the project.
In the second half of the 19th century many farmers emigrated from the rural communities of the Swiss canton of Schaffhausen, mainly due to a local agricultural crisis and better economic prospects elsewhere. There were emigration peaks around 1850, 1870 and in the 1880’s with a large majority of emigrants heading to the United States. From 1868 to 1890 an equivalent of more than 10% of the canton’s population had left, a large number for Swiss standards at the time.
Among the emigrants were many Bührers from the small hamlets of Bibern, Hofen, Opfertshofen as well as from Herblingen and Stetten in the Reiat region. Originally immigrated from southern Germany the Swiss Bührer at large remained constrained to that tiny corner of Switzerland, which greatly facilitates genealogical research.
The maps shows the Bührers’ emigration to the United States (Map 1) up to the 1880s and subsequent internal migration up to now (Map 2). Almost all of them initially immigrated to a small area in northwestern Ohio around the city of Archbold in Fulton County; some of them migrated further west to Kansas, Texas or the Pacific Northwest.
In order to provide the necessary historic context Map 1 shows historic state boundaries, population density as well as the railway network (the main mode of transportation for Swiss emigrants) at 1870, the heyday of the Bührer emigration.