QGIS

Notes for using the program

Convert polygon to points:

1. Go to the “Vector” tab.
2. Go to “Geometry Tools.”
3. Select “Extract Vertices.”

Convert points to paths (lines):

1. Use the “Processing Toolbox.”
2. Type “Points to path.”
   1. You may select “Selected features only” and/or “Created closed paths” if needed.
3. Make sure the “Order expression” is using the id’s of the vertices, and not have it blank. Use “vertex_index.”

Convert paths (lines) to polygon:

1. Use the “Processing Toolbox.”
2. Type “Lines to Polygons.”

Computer program

Getting old country borders accurately

1. Go to OpenHistoricalMap.
2. Search for country you want.
3. Go to Overpass Turbo for historical maps. OLD: https://openhistoricalmap.github.io/overpass-turbo/
4. Use this command:

nwr[“name”=“(name of country, there might be multiple aliases so check each one)”];

out geom;

	1. If it asks about "Large amounts of data", be sure to select "continue anyway".
5. Export, preferably as a GeoJSON.
6. Drag and drop file in QGIS and apply file as layers in project.
7. Get a world map in QGIS.
8. [Go to `Vector > Research Tools > Extract Layer Extent`](https://gis.stackexchange.com/questions/187215/inverting-polygons-using-qgis).
9. Create the new layer off of the world map.
10. [Go to `Geoprocessing Tools > Difference`](https://gis.stackexchange.com/questions/187215/inverting-polygons-using-qgis).
11. Select the "Extent" layer as the "Input layer" and the "World Map" as the "Overlay layer".
12. This new layer should be just the oceans an exclude land.
13. Drag and drop the GeoJSON file of the country you want from step 7.
14. [Go to `Geoprocessing Tools > Difference`](https://gis.stackexchange.com/questions/187215/inverting-polygons-using-qgis).
15. Select the country you want to fix the borders for as the "Input layer" and the oceans and water layer as the "Overlay layer".
16. Viola! You should have the country with its appropriate coastline and land borders.