Field Geometry
Submenu on "EDIT" button on
database
table form. You must enable edits
before this option is available.
- Area of each record in km²: computes area in km²
and puts in field AREA_KM2. Uses UTM, so there is a
limit to the size over which it will be valid.
- Area of each record in m²: computes area in
m²
and puts in field AREA_M2. Uses UTM, so there is
a limit to the size over which it will be valid.
- ALAND to LAND_KM2: takes Census field of land area in
square meters puts in field LAND_KM2. If the field is not
ALAND, but something like ALAND10, you will have to pick it.
- AWATER to WATER_KM2: takes Census field of land area in
square meters puts in field WATER_KM2.
- Perimeter of each record: computes perimeter in km
and puts in field PERIMTR_KM.
- Centroid of each record: computes centroid of each record
and puts in fields LAT_CENTRD and LON_CENTRD.
- Length of each record: computes length in km using the
Vincenty formulas
and puts in a field LENGTH_KM
- Polygon shape indices, using perimeter and area. Many of these are used for
Gerrymandering
- Compactness: 4piA/P^2r, iso-perimetric quotient, Polsby-Popper, Cox's circularity
- Mean width 2A / P
- Shape number (P/sqrt(A))
- Schwartzberg, 1 / (Perimeter / ( 2 * Pi * sqrt(Area/Pi)))).
Ratio of perimeter to the circumference of a circle
with the same area.
- Perimeter/Area ratio (P2A):
- Elevation change of each record
- Direction of record: line files only. Computes the azimuth from
the first point in the line to the last point.
- Distance between two points in record: must have to LAT/LONG
pairs in each record
-
Distance to line/polygon
-
Nearest point on line/perimeter
- Distance from point using
Vincenty forumula.
- Distance algorithm comparison:
does Vincenty, haversine, and cosine distance formulas
- Distance to nearest neighbor:
- Distance off map: for a points database, will add a field
DIST_OFF with the distance and direction for those records not on
the current map
- Gradient
- Point in polygon/area: find the record within an area shapefile in which a point
(or the centroid of an area/line shapefile) lies, and enter a field from
that database into the current database. For instance this could find
the county which contains a record. You want to be careful in picking
the field to insert: for counties; the FIPS are unique, but half the states
have a "Washington County".
- Sinuosity
- Number points each record
- First and last points each record. Add fields LAT_START,
LONG_START, LAT_END, LONG_END.
Last revision 5/8/2021