Welcome to Introduction to GIS Software: QGIS, Class 6
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Introduction to GIS Software: QGIS
what do you need to join two datasets?
what is the difference between the decennial census and ACS?
PUMAs
Public Use Microdata Areas
PUMAs have at least 100,000 people in them
since PUMAs are larger than census tracts, they tend to handle margin of error better
in NYC, PUMAs were drawn to roughly follow community districts
source
NTAs
Neighborhood Tabulation Area
NTAs are specific to NYC
NTAs fit within PUMAs and are made up of census tracts
since an NTA has to fit within a PUMA, it doesn't always correspond to a neighborhood's commonly known boundary
the city aggregates some census data at the NTA level
with numbers, you can do most mathematic operations
add fields with +
subtract fields with -
divide fields with /
multiply fields with *
if you need some part of your math to happen before others, use parentheses
for example,
3 + 5 * 2
for example,
3 + 5 * 2
is not the same as
(3 + 5) * 2
one solution: add another layer of the same polygons, under your choropleth
or make a rule-based style, make a "no data" rule checking for NULL
What is NULL?
a special value in most computing environments, including QGIS
source
for numbers, NULL doesn't mean zero, it means the absence of a number
source
to check for null, use IS NULL and IS NOT NULL
IN: let the field match any of these values
OR: either condition can be true
AND: both conditions must be true
you can combine OR and AND, but be careful
use parentheses if you're not sure how they will work
NOT will invert your conditions
I recommend using parentheses anytime you use NOT