The graph on the right shows the difference between the two systems in percentage of each resource that is protected as a function of the amount of money spent purchasing openspace using assessed value.

The values represent the percentage of the area protected in the web survey scoring system subtracted from the percentage of the area protected in the commissions scoring system. These values are taken from the values used in the two graphs below. More information on how the percentage of area protected was determined is on this site. When the values are positive, more of the resource protected at that point of acquisition program using the web survey's scoring system then the commissions' scoring system. For example, in the first few parcels purchased using the scoring system groundwater resources are better protected using the web survey based scoring system. This is illustrated in the graph because the purple line is above the x-axis early on.

The groups in this graph correspond to the average percentage of area protected, of all resources resource categories on the scoring page.

It is evident from this graph that the different weights given to each resource in the scoring system do not have a large impact on the amount of land that is protected in that group. For example, the agricultural group is given over twice the weight in the commissions' scoring system then in the web survey's. However, the rate at which agricultural land is protected is greater when the web survey scoring system is used, than with the commissions' scoring system. The same effect is seen for habitat resources. The greater weight given to protecting habitat resources in the commissions' scoring system is not reflected in the order that parcels are protected.

This effect is not seen for cultural resources. Twice the weight is given to cultural protection in the web survey and this seems to cause the cultural areas to be better protected when this scoring system is used. It is difficult to interpret these results as the weighting system working, because the system was not effective for the other resources.

This analysis leads one to believe that in order to see a significant difference in the order in which resources are protected, weightings have to be drastically different. This may only be true for Charlestown, and is most likely due to the large amount of co-occurring resources. The parcels considered in this analysis had an average of 5.5 resources out of a possible analyzed 14. For example, the effect discussed earlier with agricultural land may be due to the fact that many other resources overlap with these parcels. Most agricultural land also has four other resources that are contributing to it's final score. In addition the size of the parcel and the development potential of the parcel also are important. The total scoring for each parcel is as a combination of all of the individual resources. This dilutes the impact that any one resource can have on the score of the parcel.

However, it should be noted when creating weighting systems for other regions, that the differences in weighting in the scoring system may have to be very large to have a significant impact on the order that land is protected.

Finally, it is evident from the graph that the web survey's scoring system protects more resources at a greater rate then the commissions scoring system. This shows that some weighting systems may do a better job in protected all resources at a greater rate by acquiring parcels with more co-occurring resources first. It may be possible using these methods to maximize the efficiency of a openspace plan overall by assigning different weights to different resources, without impacting the order in which things are protected.

Overall it is difficult to derive any conclusions from this analysis. More analysis needs to be conducted in different geographic areas testing numerous scoring systems to better understand these effects.

The data used for this analysis can be downloaded as an Excel spreadsheet.

Difference_Analysis.xls 2.16 Mb