Spatial Thinking in Planning Practice: An Introduction to GIS

11 % Isolate: One or more categories of nominal, ordinal, interval, or ratio data can be selected, and others set aside. For example, consider a range of temperature readings taken over a large area. Only a subset of those temperatures are suitable for mosquito survival, and health o&cials can select and isolate areas based upon a speci!c temperature range that is likely there to take action in order to reduce the threat of a West Nile Virus or Dengue Fever outbreak from these mosquitoes. % Di#erence: "e di#erence of two interval level observations (such as two calendar years) can result in one ratio level observation (such as one age). For example, in 2012 (a year is an interval level value), someone born in 2000 (also interval level, of course) is 12 years old (age is ratio level, since it has a de!nite zero). % Other arithmetic operations: Two or more compatible sets of interval or ratio level data can be added or subtracted. Only ratio level data can be multiplied or divided. For example, the per capita (average) income of an area can be calculated by dividing the sum of the income (ratio level) of every individual in that area (ratio level), by the number of persons (ratio level) residing in that area (a second ratio level variable). % Classi!cation: Numerical data (at interval and ratio level) can be sorted into classes, typically de!ned as non-overlapping numerical data ranges. "ese classes are frequently treated as ordinal level categories for thematic mapping with the symbolization on choropleth maps, for example, emphasizing rank order with- out attempting to represent the actual magnitudes. "is chapter text has been compiled from the following web links that holds information with CC copyrights: use and share alike. http://giscommons.org/introduction-concepts/ http://giscommons.org/chapter-2-input/ http://2012books.lardbucket.org/books/geographic-information-system-basics/s08-02-vector-data-models.html# https://www.e-education.psu.edu/geog160/c3_p8.html Discussion Questions 1. In what ways would John Snow’s mapping process di#er given the GIS technologies available today? How would his results be di#erent or the same? 2. How do the di#erences between discrete and continuous attribute data impact the selection of using vector and/or raster data models? 3. Find an internet source that contains an interesting map that visualizes data from two of the di#erent attri- bute measurement scales: nominal, ordinal, interval, and ratio. How do the di#erent measurement scales re'ect the type of data provided? Contextual Applications of Chapter 1 All Cities Are Not Created Unequal (Brookings) American Migration Chapter 1: De!ning a Geographic Information System