A simple grid

void setup() {
  size(800, 600);
}

void draw() {
  background(#f1f1f1);
  fill(#000000);
  noStroke();
  translate(90,90);
  for (int y = 0; y < 17; y++) {
    for (int x = 0; x < 25; x++) {
      rect(x * 25, y * 25, 15, 15);  
    }
  }
}