I wanted to construct a 150km distance buffer around a city in North America. I changed the project co-ordinate system of the point to WGS84 Mercator North America from WGS 84 Lat/long to enable the buffer to be constructed in metres/km. The buffer was drawn on the map, but it doesn't show on top of local US neighbourhood census tract boundary files (which I changed to the same co-ordinate system). When I zoom to the full extent of the buffer layer, it appears to be different co-ordinbates to the census tracts layer. Am I using the correct co-ordinate system? I assume 'on the fly reprojection' is automatically turned on in QGIS3.

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    How did you "change" CRS of layers? The correct method is to reproject them using the Reproject layers tool or by exporting the layer and choosing the new CRS in the export process. The incorrect method is to change the CRS in the layer properties. – csk Apr 17 '19 at 16:14
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    Mercator is not an appropriate projection for distance calculation. The USGS Albers Equal Area would be much more appropriate for a CONUS location. Canada, Mexico, and points south would have their own appropriate projections. – Vince Apr 17 '19 at 16:16

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