Commuting Flows

Question
All those previously requesting the "Commuting Flows" data have been
using it for years, and just wanted the files.  However, I now have a
student who is hoping that I will explain its structure to her.  So, I
am hoping to have your indulgence for my ignorance and explain it to me
-- so that I can explain it to her!  Is there a user guide for these
files?

In the file for Ontario, for example (97561xcb2006008_ont.ivt) :

First line:
Total - Industry - North American Industry Classification System 2002
Total - Sex              Male
Female
Canada (01)   20000 / Ontario (35)           5134485        2559960        2574525

Last line:
Total - Industry - North American Industry Classification System 2002
Total - Sex        Male
Female
Arviat (6205015) HAM 00000 / Ottawa (3506008) C         0        0
0

I assume that the first line means that for all of Canada, 5,134,485
people commute TO or WITHIN Ontario, and that the last line means that
some number of males, between 1 and 10 in the hamlet of Arviat in
Nunavut commute to Ottawa.  Is that correct?

The table title leads me to the conclusion that the 7-digit codes are
CSD codes.  But I am puzzled by the 5-digit codes just before the / --
going from 20000 to 00000: what do they represent?

Also, given the large distances of some of these combinations, how is
"commuting" interpreted?

As I indicated initially, if there is a description somewhere that I
should be reading, to get these answers, point me to it.

Answer

1) It appears that the 5-digit codes following (20000 after Canada and 00000 after Arviat) are data quality flags.  These flags are described in detail in Beyond 20/20 if you right click on the geography variable and select the "i" icon (but please note that I don't have access to my FTP this week so I am relying on memory).

In terms of the structure, the first column is the place of residence, and the second (after the slash) is the place of work.

Please note that we are on the road this week, so I can't answer this question as completely as I'd like.  I will try to find some documentation regarding commuting flows and the rounding as soon as we can.

2)

I found the following explanation of random rounding in the Census Dictionary:

http://www12.statcan.ca/english/census06/reference/dictionary/ovpop3a.cfm#12

Random rounding

Rounding is a mathematical operation that can increase a number, decrease a number or leave it unchanged; only certain predetermined values are permitted. For example, we could decide in advance to round figures to the nearest multiple of 10, the next highest multiple of 10, or the next lowest multiple of 10. So, if we round 10, 13 and 17 to the next lowest multiple of 10, the result would be 10 in all three cases.

The random rounding method is based on established probabilities. It involves rounding every figure in a table (including the totals) randomly up or down to the nearest multiple of 5, or, in some cases, 10. For instance, random rounding of 12 to a multiple of 5 would yield either 10 or 15; applying the same operation to 10 would produce 10. This technique provides strong protection against direct, residual or negative disclosure, without adding significant error to the census data.

So your understanding of the random rounding is correct.

In terms of documentation regarding commuting, our census consultant suggests that you read the definition of commuting distance in the Census Dictionary:

http://www12.statcan.ca/english/census06/reference/dictionary/pop019.cfm (don't forget to click on "More information..." at the bottom of the definition)

Since commuting distance is derived from Question 46, you can refer to the definitions relating to that question as well:

http://www12.statcan.ca/english/census06/reference/dictionary/defbyqnum.cfm#46

Finally, you can see the actual question (46) from the questionnaire itself:

http://www.statcan.gc.ca/imdb-bmdi/instrument/3901_Q2_V3-eng.pdf