What Do Vertical Lines in Signal Graphs Represent?

[Bassalisk]

So I am 2nd year now and we started this new course Theory of Signals.

Already I bumped into a wall when it came to understand basic stuff.

Here is what I mean
[PLAIN]http://pokit.org/get/0864633c869b647116b980428a07d4f1.jpg

Here we have 4 functions, each representing one type of signal.

1st one I understand. Its a continuous function, defined at every point.

2nd one reminds me of a plotted sequence. But the thing that confuses me is that vertical line connecting abscissa and the value of the signal.

Does that line represent something? Or is it just for visual purpose?

Same question for the 3rd graph. It is even more confusing. It goes zig-zag. Again what do those vertical lines connecting 2 parts of graph represent?

 

[bob1182006]

These are the four types of signals:
1st one you got right, continuous time continuous value
2nd one is a discrete time continuous value. The lines are just there to make it easier to see at what time each point represents. In MatLab you make those plots by using stem(x,y).
3rd one is a continuous time discrete valued signal. The vertical lines just represent a jump from one value to another. The signal really is just the horizontal lines, but when you plot it the software connects the data points so you get those jumps.
4th is a discrete time discrete valued signal.

Discrete time signals can be obtained by sampling continuous time signals.
Discrete value signals can be obtained by quantization of a continuous valued signal.

 

[Bassalisk]

Thank you for clearing this confusion for me. I just finished with my math class and I still have my math goggles on. That is why I found this confusing.