This is part of a Census Bureau shapefile for
tracts.
- ALAND10 and AWATER10 are the
areas, in square meters, of the
land and water in the tract in
2010. Sometimes these will
be ALAND and AWATER. This was computed by
the Census Bureau, and used
information not present in the
shape file to determine the
proportions of land and water in
the record. (Edit,
Field arithmetic, Multiply
field by constant, or Divide
field by constant will let you
create a new field with more
understandable units;
operate on a copy of the field),
or there is an option to
automatically create it and
convert to square kilometers.
- If you use the ALAND10 field
from the shapefiles, you might want to
convert the square meters to square kilometers first (Edit,
Field arithmetic,
Multiply field by constant, or Divide field by constant). You
should probably operate on a copy of the field.
- Field SHAPE_AREA is an
ArcGIS field that has unclear
units (degrees and square
degrees), and the value does not
match that from either the
Census Bureau or MICRODEM, and
should probably not be used.
- AREA_KM2 was computed by
MICRODEM. It has no way to
know about how much of the
record is water. When
there is no water, its values
are very close to ALAND10;
otherwise it is the sum of
ALAND10 and AWATER10.
- ALAND_KM2 and AWATER_KM2
were computed by MICRODEM in two
steps: Edit,
Field arithmetic, Copy
numeric field to make a new
field, and then
Edit,
Field arithmetic, Multiply
field by constant (or divide by
constant).
If you want to compute something like
population density, you will probably want the
area of just the land, and so should use
ALAND_KM2.
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