When you see a graphed cluster of dots depicting the values and relationship of two different variables, you are seeing a visual description of relatedness called a

scatter-plot or scatter-gram

Explanation:

Scatter-plot: The term scatter-plot is also referred to as scatter-gram, scatter-graph, scatter-chatter, or scatter-diagram, and is defined as one of the types of a mathematical diagram or plot that uses Cartesian coordinates to show different values related to two variables for a particular set of data.

It is being used to determine how one variable tends to affect the other variable.

In the question above, the given statement signifies the scatter plot.

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.