2. Theory
3.2. MCA‐Step 1: Assessment of QoP
3.2.3. Transformation and Aggregation of QoP‐Indicators
Derived from the previous paragraphs, the indicators assessing QoP are highly diverse in content, meaning and background‐data and comprise both the ecological and social dimension of sustainability. Moreover, unevenly available threshold values and quality of background‐data crucially determine their qualitative or quantitative character. Figure 18 shows the challenge of integrating all indicator‐types into one assessment‐scheme and the transformation into one rank‐
scale. Derived from different dimensions and data‐backgrounds, each indicator can be associated to one of the two major scales, which determine its qualitative or quantitative character.
Figure 18 Indicator‐aggregation‐scheme (author´s draft)
Transformation
On the one hand, qualitative indicators such as the indicator “protected areas” are applied. They provide qualitative statements of the position of a housing‐site compared to the location of protected‐areas (see fig. d2 in the annex). By processing a GIS‐based overlays of both data‐sets, we derive information if a housing site is not located, entirely or partially located within a protected area. The following general statements are derived from this procedure: suitability of a site due to no overlay (value 1), limited suitability of a site due to partial overlay (value 2) and no suitability of a site as it is located entirely within a protected‐area (value 3). Whilst such qualitative indicators are not associated to pre‐determined threshold values, the provision with threshold values differs
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throughout the section of quantitative indicators (see both examples at the right columns of fig. 18).
Two different types of quantitative indicators can be described: indicators with and without predefined threshold values.256
The indicator “biotope quality” is an example for a quantifiable indicator whose threshold values need to be defined. They are determined by its upper and lower limits and provides a five‐stepped scale of possible indicator‐values from 0 (low biotope quality) to 4 (very high biotope quality). Figure 18 above highlights the further translation into a threefold classification.
Compared to that, indicators, which assess the distance to various facilities of social infrastructure are set against a set of threshold values. These threshold‐values derive from planning literature and legal frameworks as defined above. The calculations of individual buffers around the facilities of social infrastructure are executed according to distance‐standards applied in urban planning.
Therefore, a translation of these indicator‐values into a simplified threefold classification is very convenient and is based on the spatial overlay of housing‐sites and the respective distance‐buffers.
We derive information, if both sites overlay completely, partially or if they do not, which means that a housing‐site is in close, medium or large distance to the closest facility. These simplified values are derived from this procedure: suitability of a site due an entire position with the buffer of a facility (value 1), limited suitability of a site due to partial overlay with a buffer (value 2) and no suitability of a site as it is located entirely outside a buffer‐area (value 3) and therefore demands longer ways as proposed by urban planning‐standards.
The outlined measures of generalization (see also fig. 18) form the crucial step of indicator aggregation and translate both indicator‐groups to one scale. Each rank defines a value, which is later on used to quantitatively aggregate all indicators including individual weights within a Decision Support System (see chapter 3.4).
We have learnt that both data‐background and the origin of threshold‐values are highly variable within the indicator‐framework. Therefore a transfer into three outlined simplified values appears to be the best way to integrate both qualitative and quantitative indicators. It provides a comprehensive opportunity to assess each housing site according to local conditions. Moreover, an assessment of each housing‐site stating a complete, limited or no suitability facing their contribution to a sustainable and resource‐preserving settlement‐development will be enabled. This threefold distinction smoothes the consequences of the assessment and provides a more flexible approach as it does not lead to a complete exclusion of a housing‐site from the pool of future housing sites but indicates necessary revisions (e.g. modification of spatial extension of a site).
Weighting and Aggregation
To provide an integrated assessment and to derive a final QoP‐result for each of the two dimensions of QoP, the aggregation of all indicators forms the final step. The implementation of individual indicator‐weights is a necessary prerequisite to provide not only a comprehensive but also planning‐
relevant QoP‐analysis. Therefore, planners of the City of Essen have been asked to assign individual indicator‐weights, so‐called “expert‐weights”. This was explained in the preceding excursus. The
256 Further information on general indicator characteristics can be given in annex C2.
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The transformed indicator‐performances as outlined in figure 18 and the paragraphs above indicate the suitability of a site for housing purposes257 . For each indicator – qualitative and quantitative‐ the following simplified values were applied:
• Value 1 indicates an unlimited suitability and a good performance of the housing site.
• Value 2 indicates a limited suitability and a medium performance of a site.
• Value 3 indicates no suitability regarding the respective indicators and therefore a bad performance of a housing site.
Following this, an aggregation of these statements leads to final aggregated QoP‐value for both the ecological and social QoP. The aggregation of all indicators requires the expert‐weights derived from planners or the respective person executing the QoP‐analysis as discussed in the excursus above. As the aggregation then does not provide integers such as 1, 2, 3 anymore, a new translation into classes of QoP is needed in order to derive statements about a good, medium or low QoP of a housing site.
Figure 19 Indicator‐aggregation assessing QoP (author´s draft)
Following KÖTTER ET AL. (forthcoming) and the findings from the research project FIN.30, the following normative systematization of QoP‐values has been applied for an integrated QoP‐assessment: An
257 Chapter 4 and 5 will refer to this classification in terms of analysis and wording.
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aggregated QoP‐performance value of 1.00 to 1.49 indicates a high suitability as the majority of indicators show a value of 1 (high QoP and suitability). Values of >1.49 ≤ 2.49 indicate a medium suitability and QoP and values > 2.49 ≤ 3.00 indicate a low QoP and no suitability for a site according to the principles of sustainability.
The value 1.49 is defined as a threshold value for a high QoP. Its value increases, as the amount of single indicator performances of 2 (limited suitability) and 3 (no suitability) increases to such an extent, that an unlimited suitability and QoP is not given any more. The aggregated value of 2.49 indicates the threshold for a medium suitability and QoP was defined accordingly. That means, the higher the aggregated QoP‐value, the lower the actual suitability for sustainable settlement development.
The definition of equal intervals of QoP‐values was rejected as the planning oriented QoP‐
assessment is restrictive in nature, but shall also provide enough flexibility to adjust planning targets according to the outcomes of the QoP‐assessment. Restrictions are given in the classes indicating a high and a low QoP258. Only those sites will be awarded with a high QoP, as their aggregated value approaches 1.49. Also the class indicating a low QoP and no suitability is restrictive in nature. The class of medium QoP forms the largest class and follows a flexible and planer‐oriented approach:
sites of that class are not immediately to be excluded from housing development, because they still provide a limited but not overall bad suitability according to ecological and social indicators. The adjustment of a medium QoP acts as an alert and indicates single bad indicator performances. As this is the case, two kinds of adjustment can be applied by the user/ planner:
1. Spatial adjustment as a site is –for instance‐ partially located within a protected area.
2. Adjustment of expert‐weights to indicators according to local requirements. As –for instance‐ the future demographic structure of a site is adjusted to an ageing society, a limited accessibility of kindergartens, primary school or playgrounds is not of prime interest. If this is the case, the respective indicators can be assigned with lower weights. The aggregated QoP‐value will then perform differently at this site.
258 A normative definition of threshold values has been inevitable as both the number of indicators and indicator‐weights assigned by planners/ experts are flexible. The definition of these threshold values has been discussed within the research project FIN.30 together with planners from three partner communes of the consortium.
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