Legend in multiple plot in R - r

Question

According to the comments from others, this post has been separated into several
smaller questions from the previous version of this OP.
In the graph below, will you help me to (Newbie to R)
Custom legends according to the data they represent like filled for variable 1, circle points for variable 2 and line for variable 3 and their colors.
same letter size for the legend and axis-names.
The graph below is produced with the data in pdf device with following layout.
m <- matrix(c(1,2,3,3,4,5),nrow = 3,ncol = 2,byrow = TRUE)
layout(mat = m,heights = c(0.47,0.06,0.47))
par(mar=c(4,4.2,3,4.2))
#Codes for Fig A and B
...
#Margin for legend
par(mar = c(0.2,0.2,0.1,0.1))
# Code for legend
...
#Codes for Fig C and D
...

Answer 1

Using doubleYScale from latticeExtra and the data in the long format (see my previous answer), you can simplify the work:
No need to create a custom layout to superpose many plots
No need to create the legend manually
The idea is to create 2 separates objects and then merge them using doubleYScale. The latter will create the second axes. I hope I get your ploygon idea since it is not very clear why do you invert it in your OP.
library(latticeExtra)
obj1 <- xyplot(Variable~TimeVariable|Type,type='l',
groups=time, scales=list(x=list(relation='free'),
y=list(relation='free')),
auto.key=list(columns = 3,lines = TRUE,points=FALSE) ,
data = subset(dat.l,time !=1))
obj2 <- xyplot(Variable~TimeVariable|Type,
data = subset(dat.l,time ==1),type='l',
scales=list(x=list(alternating=2),
auto.key=list(columns = 3,lines = TRUE,points=FALSE),
y=list(relation='free')),
panel=function(x,y,...){
panel.xyplot(x,y,...)
panel.polygon(x,y,col='violetred4',border=NA,alpha=0.3)
})
doubleYScale(obj1, obj2, add.axis = TRUE,style1 = 0, style2 = 1)

Answer 2

Try the following:
1) For the legend part
The data can be found on https://www.dropbox.com/s/4kgq8tyvuvq22ym/stackfig1_2.csv
The code I used is as follows:
data <- read.csv("stackfig1_2.csv")
library(Hmisc)
label1=c(0,100,200,300)
plot(data$TimeVariable2C,data$Variable2C,axes=FALSE,ylab="",xlab="",xlim=c(0,24),
ylim=c(0,2.4),xaxs="i",yaxs="i",pch=19)
lines(data$TimeVariable3C,data$Variable3C)
axis(2,tick=T,at=seq(0.0,2.4,by=0.6),label= seq(0.0,2.4,by=0.6))
axis(1,tick=T,at=seq(0,24,by=6),label=seq(0,24,by=6))
mtext("(C)",side=1,outer=F,line=-10,adj=0.8)
minor.tick(nx=5,ny=5)
par(new=TRUE)
plot(data$TimeVariable1C,data$Variable1C,axes=FALSE,xlab="",ylab="",type="l",
ylim=c(800,0),xaxs="i",yaxs="i")
axis(3,xlim=c(0,24),tick=TRUE,at= seq(0,24,by=6),label=seq(0,24,by=6),col.axis="violetred4",col="violetred4")
axis(4,tick=TRUE,at= label1,label=label1,col.axis="violetred4",col="violetred4")
polygon(data$TimeVariable1C,data$Variable1C,col='violetred4',border=NA)
legend("top", legend = c("Variable A","Variable B","Variable C"), col = c("black","violetred4","black"),
ncol = 2, lwd =c("","",2),pch=c(19,15,NA),cex=1)
The output is as follows:
2) To make the font size same use the parameter cex and make it same everywhere.