Example disk-based storage of a QuadTree index. The index is built from the raw data in `data.csv`, resulting in the index txt files you see below. The index files contain pointers to their child nodes as well as a reference to the file and line number of the record. In this example, each node has a capacity of 4 data points.

-90,45,180,90.txt

nw:
ne:
sw:
se:
data.csv#5

0,0,360,180.txt

nw:-90,45,180,90.txt
ne:90,45,180,90.txt
sw:-90,-45,180,90.txt
se:90,-45,180,90.txt
data.csv#1
data.csv#2
data.csv#3
data.csv#4

data.csv