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