Add more sections + descriptions

Heads-up @agila5 I may put in a PR to improve osmextract docs based on this

Author: Robinlovelace

osm.qmd

@@ -118,23 +118,24 @@ Extracts from each provider are shown in the figures below, generated by code th
 
 ## Geofabrik
 
-`geofabrik` is a society that provides map-based services and free downloads of OSM extracts that are updated daily. 
-These extracts are based on a division of the world into different regions, covering a whole continent (plus Russian Federation): 
+`geofabrik` is a company that provides map-based services and free downloads of OSM extracts that are updated daily. 
+These extracts are based on a division of the world into different regions, at 4 different levels.
+Zones in level 1 cover a whole continent (plus Russian Federation): 
 
 ```{r}
 #| code-fold: true
 par(mar = rep(0, 4))
 plot(geofabrik_zones[geofabrik_zones$level == 1, "name"], key.pos = NULL, main = NULL)
 ```
 
-or several countries all around the world: 
+Level 2 contains polygons representing several countries all around the world: 
 
 ```{r}
 #| code-fold: true
 plot(geofabrik_zones[geofabrik_zones$level == 2, "name"], key.pos = NULL, main = NULL)
 ```
 
-Geofabrik also defines several special zones, such as Alps, Britain and Ireland, Germany, Austria and Switzerland, US Midwest, US Northeast, US Pacific, US South and US West. 
+Geofabrik also defines several special zones, such as Alps, Britain and Ireland, Germany, Austria and Switzerland, US Midwest, US Northeast, US Pacific, US South and US West (level 3).
 Moreover, it contains extracts relative to some administrative subregions, mainly in Europe, Russia, Canada and South America: 
 
 ```{r}
@@ -147,15 +148,15 @@ Check `?geofabrik_zones` and the [provider's webpage](http://download.geofabrik.
 ## Openstreetmap.fr
 
 `openstreetmap_fr` extracts are taken from http://download.openstreetmap.fr/, a web-service that provides OSM data updated every few minutes. 
-The extracts are based on several regions, such as the continents: 
+The extracts are based on several regions, such as the continents (level 1): 
 
 ```{r}
 #| code-fold: true
 # Russian federation is considered as a level 1 zone
 plot(openstreetmap_fr_zones[openstreetmap_fr_zones$level == 1, "name"], key.pos = NULL, main = NULL)
 ```
 
-or some countries around the world (less than `geofabrik`): 
+or some countries around the world (less than `geofabrik`'s level 2 zones): 
 
 ```{r}
 #| code-fold: true
@@ -217,6 +218,8 @@ The quickest way to get large OSM datasets in R (and possibly in any data analys
 
 The package makes your life easy by automating many parts of the OSM extract identification, download, and processing pipeline, so you can focus on the analysis and high-impact reasearch!
 
+## Finding an extract to download
+
 Let's see how it works for the city of Poznan:
 
 
@@ -251,6 +254,8 @@ oe_match(poznan, provider = "bbbike")
 oe_match(poznan, provider = "openstreetmap_fr")
 ```
 
+As shown above, `bbbike` is the only provide that provides a match for Poznan (the others match with all of Poland).
+
 
 # Other command line tools for working with OSM data {#sec-command-line}