And if you're running Linux, which window manager are you running?
Your program can open up a window of its own and draw graphics in that.
Or you can do the low level thing on a different virtual console using Linux's framebuffer support (see the svgalib link octopus posted above) (as an aside, press Ctrl+Alt+F2, observe what happens, then Alt+F7 to return here).
Depends on the terminal. xterm has a "tektronix mode" to emulate the old Tektronix 4014 graphic terminal. This has a 4096x4096 coordinate system for vector graphics. Most other terminals do not emulate this, of course.