Easiest way to demonstrate correlation between 2 variables graphically is by showing a scatterplot and regression line as follows:

**code:**

> ggplot(bwdf, aes(x=age, y=lwt))+ geom_point()+ geom_smooth(method='lm')

**Output (graph): **

Spider or radar plots can also be used to show correlation of one variable with all other variables:

**code:**

> library(psych)

> spider(y=1, x=2:9, data=scale(birthwt), connect=F)

**Output (graph): **

Blue lines indicate positive correlation while red lines indicate negative correlation.

**The points can be connected to show a radar plot: **

**code:**

> library(psych)

> spider(y=1, x=2:9, data=scale(birthwt), connect=T)

**Output (graph): **