This chapter talk about:  uncertainty  discusses its principles  cases and the sources of geographic uncertainty  The ways in which they operate in GIS

 It is impossible to make a perfect representation of the world, so uncertainty about it is inevitable.  Measurement error is one source of uncertainty.  Many geographic representations use inherently vague definitions.

 In many cases there are no natural units of geographic analysis.  Spatial oil:

 Uncertainty can exist both in the position of boundaries of a zone and in its attributes.  Many English terms used to convey geographic information are inherently ambiguous.  Ambiguity is introduced when imperfect indicate of phenomena are used instead of the phenomena themselves.

 Identification of homogeneous zones and spheres of influence lies at the heart of traditional regional geography as well as contemporary data analysis.  Relationships typically grow stronger when based on larger geographic units.

 uncertainty can often be conceptualized differently under field and discrete object views.  A pixel whose area is divided among more than one class is termed a mixel.  There are many reasons why measurement of position on the earth’s surface is inherently uncertain.  Difficulties in making accurate measurements from maps were a major impediment to early GIS.  Many errors in digitizing can be remedied by appropriately designed software.

 GPS is the first system that allows accurate direct and inexpensive measurement of absolute position on the earth’s surface.  Conflation combines the information from two data source into a single source.  Datasets with different lineages often reveal unsuspected errors when overlaid.  Differences in definitions are a major impediment to integration of geographic data over wide areas.

uncertainties in data lead to uncertainties in the results of analysis. Inappropriate inference from aggregate data about the characteristics of individuals is termed the ecological fallacy. The modifiable areal unit problem can be investigated through simulation of large number of alternative zoning schemes. Zoning seems similar to sampling but its effects are very different.

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