Proper data model for a 2D Tilemap (C++, Qt)

Question

I made a small 2D level editor where you can create 2D tile based maps..however, the performance inside my application is really really bad. I am currently thinking to start all over again.

The Problem is, I currently use QGraphicsItem's to represent a single tile inside a QGraphicsScene. A tile has some properties..including an image. When a map is created, I create an item for each tile which draws an image for each tile..which basically is a lot of graphicitems and it slows down the whole application. This is the function that populates a map once it is created :

    for(int i=0;i<map->m_rows;i++)
    {
        for(int j=0;j<map->m_cols;j++)
        {
            Tile* thetile=map->getAt(i,j);
            if(thetile)
            {
                if(map->getType()==twoditor::RECTANGLETILE)
                {
                    QGraphicsItem* item= new TileGraphicsItem(thetile);
                    m_scene->addItem(item);
                }
                else if(map->getType()==twoditor::HEXAGONTILE)
                {
                    QGraphicsItem* item= new HexagonGraphicsItem(thetile);
                    m_scene->addItem(item);
                }
            }
        }
    }

This works for a map with 100x100 Tiles. But if i want to create even larger maps..the loading time is really unbearable.. Can someone give me advice for a better representation of a tile map? Are there other convenient ways to show a map and edit cells(tiles) inside it?

EDIT: TileGraphicItem paint function:

void TileGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget){

setZValue(0);

if(!m_thetile->getImage().isNull())
{
  painter->drawImage(0,0,m_thetile->getImage());
}
QPainterPath circle_path;

QRect duwagrect(boundingRect().x(),boundingRect().y(),boundingRect().width(),boundingRect().height());
circle_path.addRect(duwagrect);

m_pen.setStyle(Qt::SolidLine);
m_pen.setColor(Qt::black);
m_pen.setWidth(1);
painter->setPen(m_pen);
painter->drawPath(circle_path);

if(m_thetile->getProperty()->getBlocks())
{
    QPainterPath circle_path;
    QRect duwagrect(boundingRect().x()+2,boundingRect().y()+2,boundingRect().width()-3,boundingRect().height()-3);
    circle_path.addRect(duwagrect);
    m_pen.setStyle(Qt::DotLine);
    m_pen.setColor(Qt::red);
    m_pen.setWidth(2);
    painter->setPen(m_pen);
    painter->drawPath(circle_path);
}
if(this->isSelected())
{
  QPainterPath circle_path;
  QRect duwagrect(boundingRect().x()+2,boundingRect().y()+2,boundingRect().width()-3,boundingRect().height()-3);
  circle_path.addRect(duwagrect);
  m_pen.setStyle(Qt::SolidLine);
  m_pen.setColor(Qt::green);
  m_pen.setWidth(3);
  painter->setPen(m_pen);
  painter->drawPath(circle_path);
}

if(option->state & QStyle::State_MouseOver)
{
  QPainterPath circle_path;
  QRect duwagrect(boundingRect().x()+2,boundingRect().y()+2,boundingRect().width()-3,boundingRect().height()-3);
  circle_path.addRect(duwagrect);
  m_pen.setStyle(Qt::SolidLine);
  m_pen.setColor(Qt::cyan);
  m_pen.setWidth(2);
  painter->setPen(m_pen);
  painter->drawPath(circle_path);
}

}

Answer 1

Problem is that you are showing everything even things not needed.
You should create only visible items (items in some visible region).

Another faster approach is to create custom QGraphicsItem which paints hole map, and paint only visible tiles (no tiles as sub items).