ISS Tracks do not trace circles on the flat earth map! The red dots show distances traveled in the same time. Note that the distances between two points are about 3 times greater in the southern hemisphere than in the northern hemisphere, meaning the ISS travels 3 times faster in the southern hemisphere than in the northern hemisphere.

Code

var excentr = 51.6;
var period = 360 * (1 - 15.652/360);
var nOrbits = 360 / 15;

var EarthMap = ...

var graph = NewGraph2D( {
  Id: 'JsGraph1',
  Width: '100%',
  Height: '100%',
  DrawFunc: DrawModel,
  AutoReset: true,
  AutoClear: true,
  AutoScalePix: true
} );

function DrawModel( g ) {

  g.SetAngleMeasure( 'deg' );

  var VpScaleArgs = true;
  var VpClip      = false;
  var VpLeft      = 8;
  var VpTop       = 8;
  var VpRight     = -8;
  var VpBottom    = -8;
  g.SetViewport( VpLeft, VpTop, VpRight, VpBottom, VpScaleArgs, VpClip );

  var WinXmin = -180;
  var WinXmax = 180;
  var WinYmin = -180;
  var WinYmax = 180;
  var WinWidth = 360;
  var WinHeight = 360;
  g.SetWindowWH( WinXmin, WinYmin, WinWidth, WinHeight );

  DrawEarthMap( g );

  // draw some iss tracks
  var step = 5;
  var last = nOrbits * period;
  g.NewPoly();
  for (var pos = 0; pos <= last; pos += step) {
    var lat = 90 - excentr * Math.sin( 2 * Math.PI * pos / period );
    var a = pos * Math.PI / 180;
    var x = lat * Math.cos( a );
    var y = lat * Math.sin( a );
    g.AddPointToPoly( x, y );
  }
  g.SetLineAttr( '#888', 1 );
  g.DrawPoly( 1 );

  var first = 0.9 * nOrbits * period;
  var last = first + 2.5 * period;
  g.NewPoly();
  for (var pos = first; pos <= last; pos += step) {
    var lat = 90 - excentr * Math.sin( 2 * Math.PI * pos / period );
    var a = pos * Math.PI / 180;
    var x = lat * Math.cos( a );
    var y = lat * Math.sin( a );
    g.AddPointToPoly( x, y );
  }
  g.SetLineAttr( 'red', 2 );
  g.DrawPoly( 1 );

  var first = 0.9 * nOrbits * period;
  var last = first + 2.5 * period;
  g.NewPoly();
  for (var pos = first; pos <= last; pos += 2*step) {
    var lat = 90 - excentr * Math.sin( 2 * Math.PI * pos / period );
    var a = pos * Math.PI / 180;
    var x = lat * Math.cos( a );
    var y = lat * Math.sin( a );
    g.AddPointToPoly( x, y );
  }
  g.SetMarkerAttr( 'Circle', 5, 'red', 'white', 1 );
  g.DrawPolyMarker( 3 );

}