iPhone OpenGLES Plotting Problem

Question

I started off with the default OGLES iPhone project, then I changed the Orthographic view to:

float Left = -backingWidth/2;
float Right = backingWidth/2;
float Up = -backingHeight/2;
float Down = backingHeight/2;
glOrthof(Left, Right, Up, Down, -1.0f, 1.0f);

so when I make the Vertices array I can assign the XY values of a grid without converting the range. I assign the points like this:

int current = 0;
for(int y=-backingHeight/2;y<backingHeight/2;y++) {
    for(int x=-backingWidth/2;x<backingWidth/2;x++) {
        Vertices[current] = x;
        Vertices[current+1] = y;
        current+=2;
    }
}

But the problem is that when the scene is rendered I get gaps of the background coming through in lines, its hard to explain but if you can imagine this ASCII 10x5 grid to be the screen this is what I get:

XXOXOXXXXX

XXOXOXXXXX

XXOXOXXXXX

XXOXOXXXXX

XXOXOXXXXX

Where the X are correct and O are empty spaces that shouldn't be empty!

Please help me, or ask for what other information you need and thank you very much