What is the key difference between a proportional symbol and a graduated symbol?

The distinction between proportional symbols and graduated symbols primarily centers on how they are used to represent data values and classes within a GIS context. Proportional symbols are designed to vary in size in direct proportion to the magnitude of the data being represented, allowing users to visually interpret differences in magnitude more intuitively. For instance, a larger circle might represent a higher population or sales figure, while a smaller one represents a lower figure, providing a clear visual cue regarding the relative size of different data points.

On the other hand, graduated symbols categorize data into specific classes or ranges, where each class is represented by a consistent symbol size. This means that all values within a particular range receive the same sized symbol, which can make it easier to compare these classes at a glance but doesn’t convey the specific differences in magnitude within those ranges as effectively as proportional symbols do.

Thus, the correct answer captures this fundamental aspect, highlighting that proportional symbols scale with the actual data values, while graduated symbols classify data into distinct categories represented by fixed sizes. This understanding is essential for interpreting and conveying geographic data effectively in a GIS.