I am attempting to plot in X/Y coordinates using the format for example Lat = 41100 and Y = 21400, using the coordinate system of WGS 1984 UTM zone 33N. When I plug in vector or raster data, everything is fine, but when I put in a base map, my data ends up in Africa when it should be in the UK. Can someone tell me what I am doing wrong?
Your coordinate values don't make sense for UTM in the UK, nor do they look like decimal degrees. They *might* be British National Grid, and if that's what your data frame's coordinate system is set to, that's the default used for xy (text) data. If you instead started with a base map, that would be using WGS 1984 Web Mercator (auxiliary sphere), and those values would end up near the equator around Africa.