Welcome to Methods 3, Lecture 3
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Methods 3
Projections and coordinate systems
to do this, change your project's projection
not sure which projection to use?
search in qgis
consider using projestions
source
best for New York area, many city datasets use this
source
you will encounter projections in three ways in QGIS:
- rendering (making your map look good)
- rendering (making your map look good)
- assignment (QGIS doesn't know which projection the data should be in)
- rendering (making your map look good)
- assignment (QGIS doesn't know which projection the data should be in)
- overlay (making data line up)
shapefiles
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
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 you need to change the projection of a layer to do calculations
to do this, you must save the layer with the new projection
don't change a layer's projection without saving as a new layer