In the following simple program, the canvas background is displayed, and the console log shows that I'm executing the graphics script with the proper data, but nothing is plotted.

Any ideas why not?

Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>plotTracts</title>

<link type="text/css" href="LIB\ui.theme.css" rel="stylesheet" />

  <script src="LIB\jquery-1.3.2.js"></script>
  <script src="LIB\ui.core.js"></script>
  <script src="LIB\Geometry.js"></script>


   <script>
   		canvasColor = "#ddddff";  
		mag = 1; // magnification

      function setUpCanvas(){
		canvas = document.getElementById("myCanvasTag");
        ctx = canvas.getContext('2d'); 
			ctx.fillStyle = canvasColor;
		    ctx.fillRect (0, 0, 5000, 5000);

		// PLOT THE CENSUS TRACTS
		for (var nn=1; nn<tractId.length ;nn++ ) 
		{ plotTract(nn, -1); }
	}

	function plotTract(nn, color) {    
		var x = mag * tractX[nn]; //later can center it
		var y = mag * tractY[nn];
		var r = mag * Math.sqrt(tractPop[nn]) / 5;
		ctx.strokeStyle = "#000000";
		ctx.beginPath();
		ctx.arc(x, y, r, 0, Math.PI*2, true);
		safelog(nn + ": called ctx.arc(" + x + ", " + y + ", " + r + ")");
		ctx.closePath();
color = "#ff0000";
		if (color > -1)
			{ ctx.fillStyle = color;
			ctx.fill();
			}
	}
</script>
<script>
	function safelog(msg)
	{ if (window.console) { console.log(msg); }	}
</script>

<script>
lastX=0; lastY=0; // globals to save last click loc
UpArrow=38; DownArrow=40; RightArrow=39; LeftArrow=37; //keyCodes
PageUp=33; PageDown=34; HomeKey=36; EndKey=35;

function saveCoords(e){lastX=e.pageX; lastY=e.pageY; }

</script>
</head>

<body onload="setUpCanvas()" onkeypress="keyHandler(event)" onmousedown="saveCoords(event)"> 

<script    src="tracts.js" ></script>  <!-- Load data arrays tractId, tractPop, tractX, tractY, tractAdj -->  

<canvas id="myCanvasTag" width="1000" height="1000"></canvas>

</body>
</html>