gs ls 03 misc edits

lessons/ls03_physical_features.Rmd

@@ -80,7 +80,7 @@ This lesson requires familiarity with `{ggplot2}`: if you need to brush up, have
 
 ### How to plot them? {.unnumbered}
 
-A *Physical feature map* mostly use the `color` argument.
+Using `{ggplot2}`, `geom_sf()`, and the `color` argument.
 
 #### With Categorical data {.unlisted .unnumbered}
 
@@ -98,6 +98,9 @@ ggplot(data = south_am_roads) +
 Let's create a map of the Sacramento basin in California US (`sacramento_rivers`), colored by their feature type (`FTYPE`).
 
 ```{r,eval=FALSE}
+sacramento_rivers <- 
+  read_rds(here("data/sacramento_rivers.rds"))
+
 ggplot(data = sacramento_rivers) + 
     geom_sf(aes(_____ = FTYPE), size = 1)
 ```
@@ -116,7 +119,7 @@ sacramento_rivers <-
   read_rds(here("data/sacramento_rivers.rds"))
 
 ggplot(data = sacramento_rivers) + 
-  geom_sf(aes(color = richness), size = 1)
+  geom_sf(mapping = aes(color = richness))
 ```
 
 "Richness" is the estimated number of fish species in each segment of the river.
@@ -155,7 +158,7 @@ We can complement Thematic maps with spatial *Physical features* like roads, bui
 
 ### How to plot them? {.unnumbered}
 
-As an example, we will complement a Choropleth map with the population of African countries, from the `africountries`, with:
+As an example, we will complement a Choropleth map with the population (`pop_est`) of African countries, from the `africountries`, with:
 
 -   the African trans-continental highway network lines, available in the `afrihighway` dataset from the same package.
 
@@ -180,7 +183,7 @@ This is how you plot another map layer on top of another map.
 ::: recap
 `{ggplot2}` allows to **overlap multiple layers (of maps)** from different data sources to complement Thematic maps.
 
-For this, instead of a *global* specification of data, you need to use a **local** one:
+For this, instead of a *global* specification of data, you need a **local** specification of data:
 
 ``` r
 # instead of: