In mathematics we denote maps often as
f: X\rightarrow Y
but write
y = f(x)
It's historical convention, but IMHO also intuitive if one is used to read / write from left to right.
The first notation reads easier, if one has compositions of maps
X \xrightarrow{f} Y \xrightarrow{g} Z \quad vs \quad Z \xleftarrow{g} Y \xleftarrow{f} X
the second notation reads easier, if one writes the explicit formula
y=\sin(x)\frac{x+1}{x^2+1}\quad vs \quad\sin(x)\frac{x+1}{x^2+1} = y
In computer science it's similar - most computer language use the variable on the left hand and the expression on the right hand:
z = a + b * i
d = z^2 + 2z -1
or
plot(data, xlab = "The x label", xlim=c(min(data$x),max(data$y)))
Therefore I consider the ggplot notation
aes(
x=log(t),
y=sqrt(y),
colour=as.factor(paste(height, weight)
)
better than
aes(
log(t)=x,
sqrt(y)=y,
as.factor(paste(height, weight)=colour
)
By the way: in R one can write x <- 3 + 4 as well as 3 + 4 -> x 