Index: src/uk/me/parabola/imgfmt/app/dem/DEMFile.java
===================================================================
--- src/uk/me/parabola/imgfmt/app/dem/DEMFile.java	(revision 4056)
+++ src/uk/me/parabola/imgfmt/app/dem/DEMFile.java	(working copy)
@@ -22,6 +22,7 @@
 import uk.me.parabola.imgfmt.app.ImgFileWriter;
 import uk.me.parabola.imgfmt.fs.ImgChannel;
 import uk.me.parabola.mkgmap.reader.hgt.HGTConverter;
+import uk.me.parabola.imgfmt.Utils;
 
 /**
  * The DEM file. This consists of information about elevation. It is used for hill shading
@@ -52,9 +53,43 @@
 	 * @param outsidePolygonHeight the height value that should be used for points outside of the bounding polygon 
 	 */
 	public void calc(Area area, java.awt.geom.Area demPolygonMapUnits, String pathToHGT, List<Integer> pointDistances, short outsidePolygonHeight) {
-		HGTConverter hgtConverter = new HGTConverter(pathToHGT, area, demPolygonMapUnits);
+		double top = Utils.toDegrees(area.getMaxLat());
+		double bottom = Utils.toDegrees(area.getMinLat());
+		double left = Utils.toDegrees(area.getMinLong());
+		double right = Utils.toDegrees(area.getMaxLong());
+
+		// expand HGT area for aligning with resolution 1200
+		double hgtDis = 1.0D/1200;
+		double hgtTop = Math.ceil(top/hgtDis)*hgtDis;
+		double hgtBottom = Math.floor(bottom/hgtDis)*hgtDis;
+		double hgtLeft = Math.floor(left/hgtDis)*hgtDis;
+		double hgtRight = Math.ceil(right/hgtDis)*hgtDis;
+		Area hgtArea = new Area(hgtBottom, hgtLeft, hgtTop, hgtRight);
+
+		HGTConverter hgtConverter = new HGTConverter(pathToHGT, hgtArea, demPolygonMapUnits);
 		hgtConverter.setOutsidePolygonHeight(outsidePolygonHeight);
 
+		int res = hgtConverter.getHighestRes();
+		if (res >= 1200) {
+			if (pointDistances.get(0) == -1 || pointDistances.get(0) == (int) ((1 << 29) / (res * 45))) {
+				// align area with HGT raster
+				if (res == 1200) {
+					// already calculated
+					area = hgtArea;
+				}
+				else {
+					hgtDis = 1.0D/res;
+					top = Math.ceil(top/hgtDis)*hgtDis;
+					bottom = Math.floor(bottom/hgtDis)*hgtDis;
+					left = Math.floor(left/hgtDis)*hgtDis;
+					right = Math.ceil(right/hgtDis)*hgtDis;
+					
+					area = new Area(bottom, left, top, right);
+				}
+				System.out.println("DEM aligned to HGT, resolution " + res);
+			}
+		}
+
 		int zoom = 0;
 		int lastDist = pointDistances.get(pointDistances.size()-1); 
 		for (int pointDist : pointDistances) {