Analyzing the Patterns of Space-Time Distances for Tracking the Diffusion of an Epidemic - Space-Time Integration in Geography and GIScience - page 268

Y

illness onset time

6

7

5

5

4

3

6

3

4

9

1

2

8

1

2 10

X

0

1 2 3 4 5 6 7

( X-coordinate)

Fig. 15.1 Spatial locations and onset illness of the hypothetical epidemic

Fig. 15.2 Rounded time-distance (RTD) and space-distance (RSD) two-dimensional matrix

The first step is to establish space-time distances. The time-distance (TD) is
the difference in illness onset time to detection between any two individuals (see
Eq. 15.1 ), and the space-distance (SD) is the geographic distance between any two
individuals' residences (see Eq. 15.3 ). The data D can be transformed into the SD-
and-TD two-dimensional matrix. Because the elements in the SD-and-TD matrix
are continuous values and the values cannot be accumulated, the element values
should be made discrete and grouped in intervals. In the example, the element is
integerized by rounding. The transformed rounded time-distance (RTD) and space-
distance (RSD) two-dimensional matrix is shown in Fig. 15.2 .