I am using R package `tmap` to plot maps with multiple facets, using `tm_facets()`. 

It seems like space is not maximally used: there is a lot of blank/unused space on the resulting plot. Is that a constraint due to the specific size of my maps, or can I adjust it with some parameters?

```r
library(tmap)
library(tidyverse)
data(metro)
metro_long <- metro %>% 
  gather(year, population, starts_with("pop"))

metro_long %>% 
  mutate(population = log(population)) %>% 
  filter(year %in% c("pop2010", "pop2020", "pop2030")) %>% 
  tm_shape()+
  tm_dots("population", size = 0.2, legend.is.portrait = FALSE) +
  tm_facets("year") +
  tm_layout(legend.outside.position =  "bottom" )
#> Linking to GEOS 3.6.2, GDAL 2.2.3, PROJ 4.9.3

```

![](https://i.imgur.com/YDV8V3e.png)