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Mapping with R

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CRS and Projections: Geographic and Projected CRS (01_12)

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The biggest thing to take away from this video is:

Don’t use geographic CRS for analysis

If you want to read more about coordinate reference systems, Chapter 7 of Geocomputation with R is a good place to start.

In the video I demonstrate the size of 1 degree of longitude changes dependent on latitude. For a more thorough exploration of this I recommend reading this ThoughtCo article. The mathematics of these calculations is definitely not important for your career as a maker of mapo data visualisations. But, if you’re interested in these things see here for a derivation of the degree length formula

When we used st_buffer() to draw circles around the cities we used this code:

world_cities %>% 
  top_n(10, pop) %>% 

The size of the buffer is "10" which equates to 10 degrees in CRS 4326. As we'll see in the next video, CRS 3857 is a good choice for a global projected CRS and if we wanted to draw circles with a radius of 1000km we would use this code:

world_cities %>% 
  top_n(10, pop) %>% 
  st_transform(3857) %>% 
  st_buffer(1000E3) %>% 

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