I used r software to draw a map of US state boundaries with the data of 1860, and I wanted to draw the Mississippi River on this map. I observed that the state boundary data of 1860 provided by nhgis could show the Mississippi River, but I could not separate the river line from the state line and use different colors to show it. Is there any good way to use it
IPUMS doesn’t currently provide any resources to help with this. I’m not familiar with all utilities available in R, but various GIS packages support the conversion of polygons (which NHGIS provides) to line features, which you could then edit to clip out only the lines corresponding to the Mississippi River.
Note, however, that the exact course of the Mississippi is changing constantly, and the state boundaries do not follow the current course, deviating by many miles in some cases, so the state boundaries wouldn’t effectively represent the course at a large mapping scale. The course of the Mississippi also runs within the states of Minnesota and Louisiana, so you couldn’t represent the full length of the river using state boundaries alone.
Various other data providers provide representations of water features. For example, you might get river lines from Natural Earth or from the Census Bureau’s TIGER/Line files (which are the source for NHGIS shapefiles).