cover type must be located and identified with sufficient precision to permit 

 its area to be measured or reasonably estimated. Although areas of human 

 activity also should be recorded, the energy human systems consume will be 

 measured by using social and economic data as well as the area they occupy. 



Land-use maps are a particularly good source of information but some ex- 

 hibit serious deficiencies. Although land-use maps provide minute detail on 

 human activities, the ecological systems that are not human-intensive are fre- 

 quently aggregated into categories which are not suitable for the development 

 of energetics models. For example, tidal marsh, mangroves, and other wetland 

 vegetation types are frequently shown as some catch-all category such as "wet" 

 land, or, worse, "idle" or "vacant" land. 



This step produces a map of energy producers and users and the relative 

 areas occupied by each. From this information, the energy flows of the nat- 

 ural systems can be calculated for the region. Unlike natural systems, the 

 energy flows for areas of intensive human activity do not have their energy 

 flows calculated from their total area, but instead use other measures of eco- 

 nomic activity. Methods for calculating the respective energy flows are dis- 

 cussed in Step 3. 



STEP 2: SYSTEMS BOUNDARIES 



A systems boundary must be established by the researcher at the intial 

 stages of the development of an energetics model. The boundary of the system 

 is usually dictated by the purpose of the model. It is very helpful when the 

 flow of energy across a boundary is minimized because energy flow across any 

 boundary, as well as those within the system, must be carefully itemized. In 

 many situations, the information necessary for the energetics model can be 

 more easily collected and evaluated if significant natural systems are not 

 divided. For example, a study for the National Park Service of the Redwood 

 National Park (Alexander et al . 1980a) used county lines as system boundaries 

 after the redwood habitat was mapped and found to be generally located within 

 two adjacent counties. In other energetics modeling situations, counties or 

 other political boundaries that may form an appropriate boundary seldom occur. 

 Most frequently, the decision to use political boundaries, such as county 

 lines, increases the difficulty of measuring natural systems. In the example 

 given in this paper, a model of the City of Tampa would have many more sig- 

 nificant flows across the city limits than would be necessary for a model of 

 Hillsborough County, Florida, simply because a large portion of Tampa's labor 

 force lives in the urban area surrounding the city but are largely contained 

 in Hillsborough County. 



STEP 3: IDENTIFICATION OF ENERGY FLOWS ACROSS THE SYSTEM BOUNDARY 



Once the system boundary is defined, flows of energy into and out of the 

 system can be identified. Normally these flows include solar energy in the 

 form of sun, rain, and wind; fossil fuel energy in the fonri of electricity, 

 petroleum, goods and services, and information; combinations of solar and 

 fossil fuel energy in the form of people; and money. 



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