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by: Adrain Lebsack


Adrain Lebsack
GPA 3.54


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Class Notes
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This 4 page Class Notes was uploaded by Adrain Lebsack on Wednesday September 9, 2015. The Class Notes belongs to GEOG 460 at University of Washington taught by Staff in Fall. Since its upload, it has received 20 views. For similar materials see /class/192241/geog-460-university-of-washington in Geography at University of Washington.




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Date Created: 09/09/15
Lecture 4 Levels of Measurement Learning Objectives 41 Why bother with understanding levels of measurement 42 What are the levels of measurement provided by Stevens 1946 43 Describe the levels of measurement presented by Chrisman 2002 Why did he add levels to Stevens levels Why bother with understanding levels of measurement Intelligent and ef cient design of data collection for GIS data 0 Cannot collect data without understanding measurement units and levels Interpretation of measurement 39rules39 are used to understand data and information Insight and understanding on the capabilities and limitations of geospatial data sets Provides an initial idea about understanding Fitness for use 7 are the data really what you need for this analysis Levels of Measurement Concept originates with Stevens 1946 A level is a class of measurement scales that share some common properties Stevens proposed that you could choose the correct analysis technique based on measurement levels This concept got institutionalized largely in introductory Statistics books in certain social sciences Cartographers adopted Stevens wholesale and use it to present cartographic display options Levels Nominal 7 measures classified by shared attributes characteristics Ordinal measures by orderings ranks Interval measures require a xed distance but the zero point is arbitrary Ratio 7 measure with a xed zero that means no quantity a constant interval distance on the scale What to measure The concept of a measurement scale presumes that you already know what you are measuring Most sciences have an inbuilt assumption about units of analysis What unit of something do you want to measure organisms botany amp zoology etc soil category soil science Statistics built around concept of quotpopulationsquot represented by quotsamplesquot of such individuals Central contention of Stevens and his followers Number scales determine appropriate technique for analysis A ne idea fty years ago to explain statistical options not su icient for GIS Beyond Stevens Situations not handled by Steven39s four levels as added by Chrisman Absolute Counts Cyclical Multi Dimensional Attribute Reference Systems The basic information required depends on the level of measurement Information content of attribute reference systems I Level of measurement l Information required I I Nominal I definitions of categories Ordinal definitions of categories plus ordering I Interval I unit of measure plus zero point I I Extensive ratio I unit of measure additive rule applies The rows in gray are additions by Chrisman to the classical levels of measurement articulated by Stevens 1947 Some examples in geospatial data I Time 0 Clocks calendars and their histories 0 Geologic time BCAD Greenwich Carbon dating years before present 1950 I Space 0 Horizontal 7 o coordinates 7 meters degrees minutes seconds or decimal degrees interval 0 grid sguare e g 4K is relative to paper on campus map ordinal 0 vertical 0 height above or below datum 7 feet meters interval I Attribute 0 Population count Derived scales I Spatial or Temporal or both miles per hour I Spatial m I Attribute population density year of maximum population dollars of household income per month vegetation type zoning soil bulk density Using a level of measurement depends on the use of a reference system The measurement is placed in a context for its use e g hurricane measurement T Mu Cow39le 2mg nggM 100 IsMA Table 22 Saffir Simpson Hurricane Scale PM Maximum sustained Sa ir wind speed Minimum Simpson metem surface pressure Storm surge category mph second knots millibars feet meters 1 74 96 35 42 3964 85 Greater than 980 3 5 10 17 2 97 111 43 49 84 96 965 980 6 8 18 26 3 112 131 5058 97 113 945 964 9 12 27 38 4 132 155 59 69 114 135 920 944 13 18 39 56 5 156 70 136 Less than 920 19 57 Table 23 Hurricane Damage by Category Category Level Description Example 1 Minimal 2 Moderate 3 Extensive Damage primarily to shrubbery trees foliage and unanchored homes No real damage to other structures Some damage to poorly constructed signs Lowlying coastal roads inundated Minor pier damage Some small craft in exposed anchorage torn Hurricane Jerry 1989 from moorings Considerable damage to shrubbery and Hurricane Bob tree foliage some trees blown down Major 199 damage to exposed mobile homes Extensive damage to poorly constructed signs Some damage to roofing materials of buildings some window and door damage No major damage to buildings Coast roads and low lying escape routes inland cut by rising water 2 to 4 hours before arrival of hurricane center Considerable damage to piers Marinas ooded Small craft in unprotected anchorages torn from moorings Evacuation of some shoreline residences and lowlying areas needed Foliage torn from trees large trees blownxr39II39urricane Gloria down Practically all poorly constructedr39signs 1985 Hurricane blown down Some damagertorroofing Fran 1996 materials of buildingssom39e wind and door damage Somerstructural damage to small buildingssMobile homes destroyed Serious flooding at coast and many smaller structures near coast destroyed larger structures near coast damaged by battering waves and FlnnH n Antwan Coastal Forces and Processes 59 Category Level Description Example 5 feet or less above sea level ooded inland 8 miles or more Evacuation of low lying residences within several blocks of shoreline possibly needed 4 Extreme Shrubs and trees blown down all signs Hurricane down Extensive damage to roofing Andrew 1992 materials windows and doors Complete failures of roofs on many small residences Complete destruction of mobile homes Flat terrain 10 feet or less above sea level ooded inland as far as 6 miles Major damage to lower oors of structures near shore caused by ooding and battering by waves and oating debris Lowlying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives Major erosion of beaches Evacuation of all residences within 500 yards of shore and of single story residences within 2 miles of shore possibly needed 5 Catastrophic Shrubs and trees blown down considerable Hurricane damage to roofs of buildings all signs down Camille 1969 Very severe and extensive damage to windows and doors Complete failure of roofs on many residences and industrial buildings Extensive shattering of glass in windows and doors Some complete building failures Small buildings overturned or blown away Complete destruction of mobile homes Major damage to lower oors of all structures less than 15 feet above sea level within 500 yards of shore Low lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives Evacuation of residential areas on low ground within S to 10 miles of shore possibly needed 7 subject to a variety of nonhurricane or extratropical storms Called var iously nor easters southwesters and other names depending on wind direction these winter storms can be devastating in terms of size fre quency and duration The Atlantic seaboard the Pacific coast the Gulf of Mexico and the shores of Alaska are all subject to the widespread property damage and loss of life that these storms can cause


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