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e. Planning Unit Cost Range: The range of cost values must allow the desiredinfluence on the selection of planning units. This must be considered withrelation to boundary length, as the objective function is a combination ofboundary length, boundary length modifier (BLM) and cost. The effect of theBLM will also be affected by changes in cost. If a range of costs is to be used, theBLM value should be tested with the costs in place. The Species Penalty Factor(SPF) is the importance a user puts on each target meeting its goal and alsoinfluences the selection of planning units. All of these factors have to be in correctbalance to arrive at an optimal portfolio, so the user has to decide how muchinfluence they would like each factor to have. Some planning situations requirethe cost surface to have a larger or smaller effect, and the same can be said aboutthe amount of clustering needed. The amount of experimentation on the costrange with the BLM depends on the magnitude of the boundary in comparisonwith the importance of each target meeting its goal.There are three suggested scenarios users should(Huggins, 2006):try pertaining to cost range1. Set a "flat cost" of all units set to the area of the planning unit (e.g. 260)2. Set a range of cost values with 260 as base, then going higher with the costfactors (i.e. 5* base cost) so you end up with a fairly tight range (e.g., 260- 1300).3. Set cost where managed protected areas (e.g., MPAs) offset the cost, sothat the cost in these areas is reduced by a factor (e.g. 0.33). In this case, ifyou have a planning unit where trawling activities drive the cost up, themanaged protected areas will have a lower unit cost. That way there is aquantitative difference between trawling in and out of a managed area.This should produce better results than locking in managed protected areasas a scenario.f. Boun dary Length Modifier (BLM) Experimentation: The BLM is specified inthe input parameter file using Inedit.exe. Before the boundary length of a portfoliois added to the Marxan cost function (as the boundary cost), it is scaled by theBLM. There is no theoretically good value to give it because the cost measure andthe length measure are both arbitrary (Ball & Possingham, 2000). The BLM canbe confusing to understand, but serves several important purposes:• To specify the relative importance of fragmentation in the cost function.Smaller values will make fragmentation less important than meeting goalsand minimizing area. If the BLM is set to zero, then the boundary lengthwill have no impact on the selection of the portfolio, and the output solutionwill be highly fragmented. The more you increase the BLM, the more youincrease the importance of compactness for the modeled portfolio solution.• To convert units. If the base analysis unit cost is specified as hectares andboundary length as kilometers, the BLM must serve the purpose ofconverting the boundary into comparable units.TNC Protected Area Tools (PAT) Version 3.0The Nature Conservancy, August 200948