In order to define the percent of green cover to the total area of
a roof or a podium, we used a new term green ratio. Green ratio
is distinguished from green cover. It assesses the current utilization
ratio of roofs and podiums by green spaces and can indicate
the need for additional planting. The green ratio is displayed as
the average value and coefficient of deviation (CV). The CV of the
green ratio reflects the deviation of the green ratio on an individual
roof or podium from the mean. A lower CV of the green
ratio means that there were more similar values of the green ratio
between different roofs or podiums. Population density was calculated
based on the geographical classification system of the Tertiary
Planning Unit/Street Block system (TPUs) with detailed population
data (Census and Statistics Department, 2001). The contour files
in B5000 digital maps were extracted to form elevation polygons.
We obtained information about building height directly from the
building layers of B5000 digital maps. Building area was the sum of
the areas of BP and BUP, which were calculated in ArcGIS 9.0.
Building density was calculated by the following formula based
on the TPUs:
BDi =
n
j=1
BHij · BAij)
AUi
(1)
where in the given TPU, BDi is the building density in land use i,
and is measured in meters; BHij is the building height of building
j in land use i, and is measured in meters; BAij is the building area
(including the areas of BP and BUP) of building j in land use i, and is
measured in square meters (m2); ALUi is the area of land use i, and
is measured in square meters (m2).
Because the factors were interdependent on each other, partial
correlation analysis was used to measure the roles of population
density, building density, elevation, building areas, podium areas
and building height in the spatial pattern of roof and podium gardens.