CartographyCH7

Geography
Apparent Density
the subjective response to the physical stimulu of the actual density of the objects in a visual field
Center of Gravity Principle
Placement of the dot in its territorial domain in the way that best represents all the individual elements in the domain.
Coalescence
merging of the dots in dense areas; the visual integrity of individual dots is lost
Dot Density Mapping
method of producing a map whose purpose is to communicate the spatial variability of density of discrete geographic data; also simply called dot mapping
Dot Polygon
the area represented by each dot on a dot map, also referred to as the dot’s territrial domain
Dot Value
the numerical value represented by each dot in dot mapping, sometimes referred to as unit value
Locational Filter
ancillary data layers or maps that influence the placement of dots within the enumeration units
Numerousness
the subjective response to the physical stimulus of the actual number of objects in a visual field; not the result of the conscious ativity of counting; number is underestimated reading dot maps
Spatial Proxy
the dot’s function of representing geographical space
Mapping Technique

1. use point symbols for quantitative data

2. Symbol form consider size, shape, color, and the frequency of dots

3. works best for enumeartion area totals, dot locations, ancillary data and dot locations

Advantages of dot density map

1. easily understood

2. good way to display variations in spatial density

3. original data may be recovered from the map

4. more than one data set may be illustrated

5. GIS and mapping software implementation

Disadvantages of a dot density map

1. reader perception is not linear

2. GIS will randomize dots within enumeration units

3. ancillary data layers or imagery doesn’t control dot placement

4. large ranges in data values aren’t acceptable

5. practically impossible to recover original data values when them map is designed for optimum portrayla of relative spatial density

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