Welcome to Methods 3, Lecture 6
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Methods 3
Sana
updating attribute tables
deleting fields
sometimes you need to do something more complex
double-click to rename
refactoring always makes a new layer that you should save to a shapefile
the field calculator
the field calculator is a way to create new columns
column types
- numbers: integer, real (decimal numbers)
- text: string
- dates: with and without time
mathematical expressions
+, -, /, *
mathematical expressions
+, -, /, *
add, subtract, divide, multiply
sometimes it is useful to convert a column type
if med_income is -, make the new column NULL, else convert to an integer
geocoding
"I have this spreadsheet I want to map..."
"...it has addresses but doesn't have coordinates"
geocoding is a business
Google's geocoding terms:
up to 2,500 geocoding requests per day
Google's geocoding terms:
If you're using it online, "The Geocoding API may only be used in conjunction with a Google map..."
source
Yahoo's geocoding terms:
up to 2000 geocoding requests per day
Yahoo's geocoding terms:
"You must not store any results"
source
watch out for the "null island" effect
if geocoders can't find a location, they sometimes default to the middle of the country/state
source
sometimes if geocoders really have no clue, they give 0,0
source
also, since most geocoders have limits you often need to break up your data into smaller files
what about going from a point → name of location?
"Never mind so-called disputed places (Kashmir, the West Bank, Cyprus, etc.) all neighbourhoods are 'disputed' around the edges..."
"... Our experience has been that there are few better ways to pick a fight than to tell someone what neighbourhood they are in (and being wrong)."
Aaron Straup Cope
first, create a grid
then, use Count Points in Polygon to find the count per hexagon
heatmaps
heatmaps attempt to show probability over an area
source
heatmaps look at the covered area as a raster made of pixels
source
radius: the area around a point that point influences
rows and columns: the resolution of the output raster, in pixels
style with singleband psuedocolor
consider a rectangle with a gradient fill instead
there are a variety of methods for giving values to pixels
Creating data
