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Dasymetric Tessellaton

Dasymetric Tessellaton

What if You Shade a Polygon and No One can see it?
or
Bigger Might be Better

Walter Kent Tierchen
State of Minnesota

#nacis2015

Nathaniel V. KELSO

October 16, 2015
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  1. Dasymetric  Tessella.on  
     
    What  if  You  Shade  a  Polygon  and  No  
    One  can  see  it?  
    or  
    Bigger  Might  be  Be

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  2. Tessella>on  
    •  A  >ling  of  regular  polygons  
    hon.html  

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  3. Dasymetric  Mapping  
    A  is  organized  by  a  large  or  arbitrary  area  
    unit  is  more  accurately  distributed  within  that  
    unit  by  the  overlay  of  geographic  boundaries  
    that  exclude,  restrict,  or  confine  the  aques>on.  
    honary/term/dasymetric%20mapping  

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  4. What  problem  are  you  trying  to  solve?  
    •  Some  polygons  are  too  small  to  see  
    •  Possible  solu>ons  
    – Hand  out  magnifying  glasses  
    – Really  big  paper  
    – Delete  small  polygons  
    – Use  a  standard  size  for  all  small  polygons  
    – Buffer  small  areas  
    •  Overlapping  buffers  
    •  Topology  errors  

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  5. •  2,800  ci>es,  townships  and  unorganized  areas  
    •  From  1/10th  of  a  square  mile  to  over  1,000  square  miles  
    •  Average  size  30  sq  mi  
    •  The  maps  were  correct  but  difficult  to  see  small  areas  
    •  Choropleth  issue  
    •  Density  higher  in  ci>es  and  size  did  not  represent  taxpayers  impacted,  typically  an  
    inverse  ra>o  
    •  Select  size  and  shape  of  tessella>on  
    •  Tried  all  three  regular  tessella>ons,  triangle,  square  and  hexagon.  
    •  Joe  Berry  stated  that  hexagon  was  the  best  way  to  represent  maps.  
    •  Tessella>on  size  was  trial  and  error,  needed  to  be  small  enough  to  represent  the  
    smallest  polygon  in  the  layer.  
    •  Too  small  would  result  in  millions  of  extra  cells  
    •  Limita>ons;  ci>es  bounded  by  other  ci>es  (metro  areas)  could  not  be  enlarged,  
    shape  is  not  maintained,  small  areas  easier  to  see,  but  s>ll  small  

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