Understanding some interesting patterns in a scatterplot I made a scatterplot for some random variables and they turned out to be interesting patterns. I checked google to learn how to interpret patterns in scatterplots but I failed to find things that match the patterns I have. 
I know that a linear relationship appears as a line. I also know that a non-linear relationship appears as a curve or some kind of shape. However I'm skeptical about how to interpret the patterns in my plots. Are they non-linear relationships? Or just moderate-to-weak positive linear relationships?
Here are the interesting patterns I found.
Pattern 1:

Pattern 2:

Pattern 3:

Pattern 4:

For Pattern 1 all I could think of is that it is a weak linear relationship. Pattern 2 looks like a vertical line to me, so is that a strong linear relationship between the two variables? Pattern 3 and 4 are the strangest for me. All I can think of is that they are non-linear relationships. Is that true?
 A: I think I'd agree that 1 is a weak positive linear relationship and, like whuber said, 2 will make more sense on a log scale. 3 and 4, however, seem like perfect candidates for ANCOVA. You can see that there are basically 2 separate linear relationships within the same scatter plot. That seems to indicate that there is another variable that controls which of those two linear relationships you end up with.
Suppose we consider an experiment where students are subjected to learning math from a good teacher or from no teacher at all and we have theie pre class math scores and their post class math scores. We then look at a scatter plot of preclass scores to post class scores. We would expect preclass scores to have a high positive correlation with post class scores but we would also expect that students in the good teacher treatment would score better than students in the no teacher treatment. This could give us a plot that looks very similar to plot 3. The relationship of pre to post is still linear within treatments but depends highly on which treatment they recieved. This kind of relationship can be modeled by ANCOVA.
