Procedures for computing WRB household density  Allan Branscomb, Aug 27, 1998

Source data set is /ise3/wrb/stf1b, product is /ise3/wrb/hhdeng

Attributes used:

 p100p2		the area weighted population of clipped census block
 hibx0001	number of households in block
 area		the area of the clipped census block
 oldarea	the area of the block before it was clipped 


Household density is computed (using Arcview) from the area weighted number of 
households and the clipped area in acres, not from the number of persons
per household calculated above.  For households per acre:

	hhdenac = (hibx0001 * (area / oldarea)) / (area * 0.0002471054)

Sum: 108762.5
Count: 46077
Mean: 2.4
Maximum: 468.5
Minimum: 0.0
Range: 468.5
Variance: 42.5
Standard Deviation: 6.5

The very large densities arise from very small areas, e.g. the maximum value
arises from a census block (county 039, block 36306) whose area is 15.7 sq m
with a population of 5 and two households.  This is not a clipped census block.



A new field, pphh - persons per household, is computed with an area weighted
household count :

	pphh = p100p2 / (hibx0001 * (area / oldarea))

Sum: 90320.9
Count: 33146
Mean: 2.7
Maximum: 965.0
Minimum: 0.0
Range: 965.0
Variance: 53.6
Standard Deviation: 7.3

Of the 46,077 census blocks or portions of blocks in the WRB, 46 have pphh
greater than 20.  One of these blocks lies on the periphery of the basin
at the Sandy watershed boundary and had 90% of its area within the basin.  
They appear to contain apartment buildings and residence hotels.  This
step was done as a confidence check of the data and because it may be
useful in other applications.

The hhdenac field is gridded:

Grid: show setcell
30
Grid: show setwindow
440445         4800375        606195         5087325
Grid: hhdeng = polygrid (stf1b, hhdenac)
 Converting polygons from STF1B to grid HHDENG
Number of Rows    = 9565
Number of Columns = 5525

Grid: describe hhdeng
                           Description of Grid HHDENG

Cell Size =              30.000         Data Type:            Floating Point
Number of Rows    =        9565
Number of Columns =        5525

           BOUNDARY                                STATISTICS

Xmin =               440445.000         Minimum Value =                0.000
Xmax =               606195.000         Maximum Value =              323.700
Ymin =              4800375.000         Mean          =                0.094
Ymax =              5087325.000         Standard Deviation =           0.843

                          COORDINATE SYSTEM DESCRIPTION

Projection                  UTM
Zone                         10
Units                    METERS             Spheroid             CLARKE1866



Hhdeng is stored in /ise3/wrb