Nathaniel V. KELSO
October 16, 2015
120

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

October 16, 2015

Transcript

1. Dasymetric  Tessella.on     What  if  You  Shade  a  Polygon

and  No   One  can  see  it?   or   Bigger  Might  be  Be<er

3. Dasymetric  Mapping   A<ribute  data  which…      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  a<ribute  in   ques>on.   h<p://support.esri.com/en/knowledgebase/GISDic>onary/term/dasymetric%20mapping
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
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