Welcome to Methods 3, Lecture 5
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Methods 3
clipping?
Ashley
Jason
project proposals due next week
project proposals
- more about your topic
- work plan
- what can you get done by the milestone (11/8)?
see the Final Project assignment in Canvas for links to past years' projects, expectations
joins
attribute joins
joins relate two datasets to each other
joins create new hybrid datasets
source
"I have this spreadsheet I want to map..."
you need a file with relatable geographies
usually these are IDs of some sort
and a column in each file that relates the two
open the layer properties on the layer you want to add data to
this is almost always the spatial layer (shapefile or otherwise)
go to the joins tab and add a new one
join layer: the spreadsheet you're getting data from
join field: the field to join with from the spreadsheet
target field: the field to join with from the spatial layer
what is the census?
decennial census
American Community Survey
margin of error: higher with 1-year estimates and smaller geometries
no matter which data you download, you'll need appropriate geographies to go with it
census blocks are the smallest area data is aggregated to
source
blocks
block groups
tracts
tracts have population between 1,200 and 8,000, optimally 4,000
source
NTAs are NYC-specific aggregations of census tracts
source
downloading census data
joining census data
make sure you have the right boundary files
source
join on the columns that line up with each other
in this case, either
AFFGEOID and GEO.id or
GEOID and GEO.id2
spatial joins
spatial joins
when you have layers that both have geographic features
Works best when you have:
- polygons that don't overlap (such as school districts or census tracts) and
- points or smaller polygons that fall within them