Nathaniel V. KELSO
October 16, 2015
96

# 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

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

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

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