Which best characterizes a tree map?
1) The visualization of a tree of quantitative values as a hierarchy of rectangles where rectangle area corresponds to data value
2) The simplification of a tree to its essential backbone by removing nodes with low betweenness centrality
3) The regions on a graphical choropleth map shaded green to indicate forests
4) The visualization of a tree where the root node is placed at the center of a circle and the leaf nodes are positioned on the circle