What would it mean for space to be one-dimensional? It would be similar to 1D time. Imagine a clock, except that instead of marking durations, it marks distances. It’s like an odometer for a vehicle that moves at a constant speed and never stops. Like this with units of distance (metres, kilometres, miles, etc.):
Imagine a spacecraft has been sent on a trip that will extend beyond the solar system (like Voyager 1 or 2), and there’s an online odometer of how far it has traveled so far. That’s what 1D space looks like. You could say, “The spacecraft was at 42000 gigametres from the sun as I completed kindergarten. That was many kilometres ago. Here’s it’s at 48375 Gm.”
A point on the Earth’s equator travels 40,075 km per day. Hours could be marked as 1/24th of this travel distance, or 1670 km per hour. “What distance is it?” could replace “What time is it?”
The 1D space + 3D time duration has two transformations, similar to the Galilean and the Lorentz transformations. In the Galilean-like 1D space + 3D time duration is absolute: everyone marks the same position in space, everyone is using the same distance “clock”. I call it a “odologe,” which combines odo(s) + (horo)loge because it keeps a path counter running the way a clock keeps time. See here for more information.