Table 3. Proportion of surnames classified as local depending on different exclusion criteria.

	Proportion
Population	MLQ>19, dist<83 km	MLQ>19, dist<120 km	MLQ 19	MLQ>45, dist<83 km	MLQ>45, dist<120 km	MLQ 45	MLQ>120, dist<83 km	MLQ>120, dist<120 km	MLQ 120	MLQ 200	MLQ 300
Cornwall	0.550	0.583	0.767	0.467	0.483	0.533	0.417	0.433	0.467	0.267	0.217
Cumbria	0.345	0.397	0.552	0.293	0.293	0.328	0.190	0.190	0.190	0.086	0.034
Devon	0.316	0.354	0.684	0.316	0.342	0.456	0.253	0.266	0.316	0.152	0.076
Forest of Dean	0.164	0.299	0.478	0.149	0.209	0.239	0.090	0.134	0.149	0.119	0.045
Kent/Sussex	0.469	0.469	0.653	0.429	0.429	0.490	0.388	0.367	0.408	0.204	0.122
Lincolnshire	0.367	0.433	0.667	0.367	0.400	0.567	0.267	0.267	0.333	0.133	0.067
North East	0.324	0.382	0.588	0.309	0.338	0.485	0.096	0.103	0.154	0.088	0.044
Norfolk	0.430	0.440	0.700	0.400	0.410	0.520	0.230	0.240	0.270	0.150	0.120
Pembrokeshire	0.436	0.487	0.590	0.231	0.256	0.359	0.103	0.103	0.128	0.051	0.051
Oxfordshire	0.278	0.316	0.582	0.241	0.266	0.380	0.190	0.203	0.266	0.165	0.101
Yorkshire	0.372	0.414	0.621	0.248	0.269	0.379	0.090	0.103	0.138	0.083	0.034
All populations	0.363	0.411	0.625	0.309	0.333	0.431	0.186	0.200	0.236	0.131	0.077

The two main criteria were a minimum location quotient (LQ) of the district with the highest LQ (MLQ) and maximum distance of the mean grandparental place of birth (MGP) from that district for each sample. When no distance is given, the distance constraint was not used. A number of samples were further excluded because of observed multiple peaks or broad geographic surname distributions (see Supplementary Table 3). These exclusions are incorporated into the proportions here.