Welcome to Methods 3, Lecture 3
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Methods 3
best for New York area, many city datasets use this
source
for now, try to remember the codes 2263 and 4326
you will encounter projections in three ways in QGIS:
- rendering (making your map look good)
- rendering (making your map look good)
- assignment
- rendering (making your map look good)
- assignment (when QGIS doesn't know which projection the data should be in)
- rendering (making your map look good)
- assignment (when QGIS doesn't know which projection the data should be in)
- overlay
- rendering (making your map look good)
- assignment (when QGIS doesn't know which projection the data should be in)
- overlay (for some calculations)
vector spatial data types
vector spatial data types
- shapefile
- geojson
- geopackage
- KML
- CSV
- ...and others!
if you're unsure, download the file and drag and drop into QGIS
shapefiles
shapefiles are very common
shapefiles have some annoying properties
1. column names limited to ten characters
how do you pronounce "C_DIG2DESC"?
2. multiple files make up a shapefile
3. one geometry type per shapefile
despite it all, shapefiles are still by far the most common spatial data format
but CSVs are common and handy for point data
these are simply text files
comma separated values
if a CSV has coordinates as two separate columns, you can open that in QGIS
QGIS doesn't know what the projection of a CSV is, so you need to help it out
Attributes
Selection
thematic maps
thematic maps focus on a theme or subject
vs reference maps
qualitative vs quantitative
in maps:
in maps:
qualitative → categories
in maps:
qualitative → categories
quantitative → numbers
qualitative thematic maps categorize features' attributes
quantitative thematic maps use features' numeric attributes
quantitative thematic maps
aka choropleth maps
choropleth
choro: region
pleth: multitude
how do you decide which regions are given which styles?
you make up categories for ranges of values
the Modifiable Areal Unit Problem
the Modifiable Areal Unit Problem
the shapes you use can influence the way your data looks without changing the data
sometimes it will help to export a file to a shapefile before doing calculations
Finding data