Complex sentence: In the 21st Century the majority of these are in the form of diagrammatic representations of the system but some cities prefer to show their transit system on highly detailed topographic or 3D maps of the entire urban area.
Split into simpler sentences: In the 21st Century, the majority of these are in the form of diagrammatic representations of the system. However, some cities still prefer to show their transit system on highly detailed topographic or 3D maps of the entire urban area.