How Poland Drifted to the West

Today's #30DayMapChallenge is Polygons.At the risk of starting World War III, I've created a map of Poland's Historical Borders. The map uses polygons to show how Poland's borders have changed at different points in its history. The historical boundaries were downloaded from OpenHistoricalMap.The map includes three snapshots: the semi-autonomous Congress Kingdom of Poland in 1815, the Second Polish Republic immediately before the German and Soviet invasions of 1939, and the post-war borders established in 1945. But rather than simply displaying these three historical boundaries, I thought it would be interesting to use turf.js to calculate how much territory Poland has gained and lost between these different periods.Turf.js provides the spatial analysis behind three additional map layers. Using its polygon operations, I first calculate the area shared by all three historical boundaries, which I've called Common Ground. I then combine the 1815 and 1939 territories and subtract the 1945…

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