Distribution of Data - Spatial Mathematics: Theory and Practice through Mapping - page 178

Figure 8.4 Tornadoes in Colorado—lower on the Fujita scale. Source of base map:
Esri software.
What areas of the country experience the most frequent tornadoes? In other
words, as manifested on the map, which areas of the country have the densest
pattern of tornadoes? Does it change any of your stereotypes about tornadoes?
Contrary to popular opinion, Kansas does not appear to be the primary candi-
date for the most frequent and densest tornado activity, but rather, Oklahoma.
Tornadoes are not damaging simply because they touch down, but in large
part because they move across the landscape, tearing up land and infra-
structure as they do so. Therefore to fully understand the phenomenon
spatially, it is necessary to examine tornadoes as tracks and not as points.
For example, examine the map in Figure 8.5 , showing tornadoes mapped as
tracks where the track data are known, with an arrow indicating the direc-
tion of movement. What spatial patterns do you notice to the length and
direction of the tracks? You should detect a southwest-to-northeast move-
ment of most of these tornadoes, no matter where in the country you are
looking. Numerous exceptions exist, but this direction fits with the prevail-
ing wind direction and the jet stream across North America. Measuring the
mean direction of the tornadoes on this map, in a 25 mile radius around Ann
Arbor by cardinal direction, reveals a direction of approximately 60, or 60
degrees east of north, which is a northeast-tending-to-due-east direction. An
analysis of the track length of these tornadoes reveals the mean track length
as eight miles (12.9 kilometers).