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Generator. This tool creates all the necessary fields and dissolves each target layerso there is one table listing for each unique target type.2. Cost Surface. This is also an optional layer, but required if the user is going toinclude a “Unit Cost” measure to each planning unit as indicated in the Marxanalgorithm. Any number of measures may be used such as threat or suitability forconservation strategies, or a surrogate for actual cost, such as area. TheEnvironmental Risk Surface (ERS) module can be used to create customized gridswhich can be summarized at the planning unit and used as a cost measure.Marxan attempts to minimize the total portfolio cost by selecting the fewestplanning units with the lowest total unit cost needed to meet all biodiversity goals.The Marxan Input Generator allows users to assign cost to each planning unit byextracting values from a grid, using an existing planning unit field, taking the areaof the planning unit, or typing in a flat cost that is assigned uniformly to allplanning units.3.4.Planning Units. These are the units that house all the necessary information forMarxan to run and allow comparison and selection between candidate areas.Planning units can be systematic units such as hexagons; or unsystematic subdivisions of the landscape such as watersheds or administrative boundaries. Thesize of the units should be representative of the scale of analysis and input dataresolution. For users who would like to use hexagons as planning units, theHexGen tool is available in the Marxan Tools drop-down menu.Protected Areas or Special Interest Areas. This is an optional layer, used inMarxan for what is called the ‘Status Layer” or ”Status Identifier.” This layermust be a polygon feature class and is required if the user plans to run a scenariowhere the planning units that overlap declared protected areas or special interestareas are to be “locked-in” or fixed in the reserve, thus always included in thesolution. These planning units are first considered when Marxan attempts to meetthe conservation goals. If goals are met within these areas, no additional planningunits are selected for that particular target goal. The Marxan Input Generatorpermits users to specify a status layer to use when assigning the identifier. Userscan also specify a field in an existing planning unit attribute table.TNC Protected Area Tools (PAT) Version 3.0The Nature Conservancy, August 200950