No. The distance of a line on a graph will not affect how steep it is. Distance does not affect slope.
With distance on the x axis and time on the y axis a steep line would indicate a short distance traveled over a long period of time, depending on the scale of the graph.
It means that the speed of the object is constant.
What does a steep looks like
It means that as time goes on, the distance increases quickly.
It means you are going very fast
It looks for all the world exactly as if it were a steep line.
Yes. Speed is the rate at which distance changes over time. In calculus terms v = dx/dt, or the slope of the distance vs. time graph. If the slope of the distance vs. time graph is a straight line, the speed is constant.
The diagonal lines show how the values change over time, also known as a trend
Well, no. If the graph is a straight diagonal line, then the DISTANCE is steadily increasing, not the speed. This would translate into a constant speed. If the speed is steadily increasing, the object would travel more distance per unit time as we move along the horizontal axis. Meaning, the graph would curve upward.
It means that either the distance is measured from the starting-line and the object is moving forward, or else the distance is measured from the finish-line and the object is moving backwards, because the distance is growing as time goes on. If the upward sloping diagonal line is straight, it means the speed is constant. (not velocity)