(On the extremely close-up image here, you can see jaggedness on the lines. That seems to be a pattern in the phosphor screen. I don't know why it's there. I've seen other vector displays that do not exhibit this. Perhaps it's from aging or burnt phosphor?)
Because the terminal did not have to store a bitmap of the display, it could be very high resolution. The standard tek4013 had a resolution of 1024 x 768. An extended precision option increased that to 4096 x 3072! Obviously the diameter of the smallest dot the electron beam could display was much larger than 1/4096 the size of the screen, so you could not get that sort of resolution if you tried to dump a bitmapped image to the screen, but if you were drawing lines and curves, you could place objects with that high resolution.
The tek4013 can be used as an ASCII or as an APL terminal. It has an ASCII/APL rocker switch just above the keyboard. All keyboard keys have both character sets printed on them. APL is a math-oriented programming language that requires a special character set which consists of mathematical symbols.