Geography Reference
In-Depth Information
eliminate expert subjectivity in cartographic generalization process. There is no
doubt that expert skills are crucial in cartographic generalization, but shape metrics
could serve them as a “statement of fact” to support their expert knowledge. Thus,
shape metrics are suitable to help cartographers with decisions about the level of
generalization.
In this paper, we applied shape metrics calculation on 22 levels of cartographic
generalization in the sense of reducing the complexity of mapped features to obtain
quantitative characteristics of generalized shapes of four building ground planes.
Our idea was to evaluate results of cartographic generalization in the sense of
reducing the polygon complexity by examining the shape metrics values of each
generalization level. We believe that this approach could show deviations or mis-
takes in the process of semi-automated generalization. This pilot study showed
great potential for quantitative description of generalization outputs. In addition,
there are some recommendations about particular shape metric usability.
Data and Methods
Cartographic geometry generalization and shape metrics calculations were
performed on four buildings ground plans. First, the ground plans were vectorized
in GIS upon ground plans of four architectonically different buildings with distinc-
tive shapes:
• Petronas Towers (Kuala Lumpur, Malaysia)
• Lund University main building (Lund, Sweden)
• Houses of Parliament (London, United Kingdom)
• Church of St. Maurice (Olomouc, Czech Republic)
ground plans are depicted in Fig.
1a
. All ground plans were adjusted
to uniform size of the X-axis (thus their shapes do not corresponds to their real size
and therefore the units in shape area and length indexes are not relevant although
being calculated in square meters, and meters, respectively) in order to ensure
comparable shape simplification in particular generalization levels.
Then, the ground plans were generalized using Simplify Building tool available
in ESRI ArcGIS for Desktop. The algorithm hidden behind this tool reduces details
in the boundaries of buildings, while maintaining the essential shape and size of the
buildings. The simplification process preserves and enhances orthogonality of
buildings. Building simplification is for applications at large scales, where build-
ings are still represented individually. It works on an entire building boundary, not
on selected segment of it. The number of vertices will be reduced, but the measured
area will remain roughly the same as the original. The maximum degree of
simplification is reached when a building is reduced to a rectangle (Lee and
Hardy
2006
).
The generalization was done in 22 levels corresponding following simplification
tolerances: t
Buildings
'
2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 80, 100, 200,
¼
