title: How to define fixed aspect-ratio for (base R) scatter-plot
body: <p>I am plotting correlation coefficients (values = 0.0:1.0) for two isotopes measured in each individual from two populations. I would like to have a fixed aspect-ratio for my scatter-plot so that the x- and y-axis are exactly the same size no matter the graphics device. Suggestions?</p>
  
  <p>This is my first plot in R, any comments on refinements to my code is appreciated? Finally, is it worth investing in learning the basic plotting techniques or should I jump right to ggplot2 or lattice?</p>
  
  <p>My plot script:</p>
  
  <pre><code>## Create dataset
  WW_corr &lt;-
  structure(list(South_N15 = c(0.7976495, 0.1796725, 0.5338347,
  0.4103769, 0.7447027, 0.5080296, 0.7566544, 0.7432026, 0.8927161
  ), South_C13 = c(0.76706752, 0.02320767, 0.88429902, 0.36648357,
  0.73840937, 0.0523504, 0.52145159, 0.50707858, 0.51874445), North_N15 = c(0.7483608,
  0.4294148, 0.9283554, 0.8831571, 0.5056481, 0.1945943, 0.8492716,
  0.5759033, 0.7483608), North_C13 = c(0.08114805, 0.47268136,
  0.94975596, 0.06023815, 0.33652839, 0.53055943, 0.30228833, 0.8864435,
  0.08114805)), .Names = c("South_N15", "South_C13", "North_N15",
  "North_C13"), row.names = c(NA, -9L), class = "data.frame")
  
  opar &lt;- par()
  
  ## Plot results
  par(oma = c(1, 0, 0, 0), mar = c(4, 5, 2, 2))           
  plot(1,1,xlim=c(0:1.0), ylim=c(0:1.0), type="n", las=1, bty="n", main = NULL,
       ylab=expression(paste("Correlation Coefficient (r) for ", delta ^{15},"N ",
                       "\u0028","\u2030","\u0029")),
       xlab=expression(paste("Correlation Coefficient (r) for ", delta ^{13},"C ",
                       "\u0028","\u2030","\u0029")))
  
  points(WW_corr$South_N15, WW_corr$South_C13, pch = 23, cex = 1.25, 
         bg ="antiquewhite4", col = "antiquewhite4")
  points(WW_corr$North_N15, WW_corr$North_C13, pch = 15, cex = 1.25,
         bg ="black")
  axis(1, at = seq(0, 1.0, by = 0.1), labels = F, tick = TRUE, tck = -0.01)
  axis(2, at = seq(0, 1.0, by = 0.1), labels = F, tick = TRUE, tck = -0.01)
  abline(h=.86, v=.86, col = "gray60", lty = 2)
  legend("topleft", c("North", "South"), pch = c(15, 23), 
         col = c("black", "antiquewhite4"), pt.bg = c("black", "antiquewhite4"),
         horiz=TRUE, bty = "n")
  
  par(opar)
  </code></pre>