@Override
    String getFileName(double lat, double lon) {
        int intKey = calcIntKey(lat, lon);
        String str = areas.get(intKey);
        if (str == null)
            return null;

        int minLat = Math.abs(down(lat));
        int minLon = Math.abs(down(lon));
        str += "/";
        if (lat >= 0)
            str += "N";
        else
            str += "S";

        if (minLat < 10)
            str += "0";
        str += minLat;

        if (lon >= 0)
            str += "E";
        else
            str += "W";

        if (minLon < 10)
            str += "0";
        if (minLon < 100)
            str += "0";
        str += minLon;
        return str;
    }
@Test
    public void testGetFileString() {
        assertEquals("Eurasia/N49E011", instance.getFileName(49, 11));
        assertEquals("Eurasia/N52W002", instance.getFileName(52.268157, -1.230469));
        assertEquals("Africa/S06E034", instance.getFileName(-5.965754, 34.804687));
        assertEquals("Australia/S29E131", instance.getFileName(-28.304381, 131.484375));
        assertEquals("South_America/S09W045", instance.getFileName(-9, -45));
        assertEquals("South_America/S10W046", instance.getFileName(-9.1, -45.1));
        assertEquals("South_America/S10W045", instance.getFileName(-9.6, -45));
        assertEquals("South_America/S28W071", instance.getFileName(-28, -71));
        assertEquals("South_America/S29W072", instance.getFileName(-28.88316, -71.070557));
    }