The remarkable fact that people who work on understanding our DNA always mention in their talks is that we have about 1.5 m of DNA in the nucleus of each of cells, and these nuclei are only around 5 thousandths of a millimetre across. That is a lot of DNA in a small space. Stretched out the DNA is longer than some of us are tall, but this DNA is crammed into a space too small to see with the naked eye.
We all have 46 chromosomes worth of DNA in each of our cells. Each one is kind of a stringy object that is typically around a few micrometres across, and all 46 are squeezed into a cell nucleus that is itself maybe only 7 micrometres across. These chromosomes are surprisingly variable. Chromosome number 18 has maybe 250 genes on it, while number 19 has around 1,500 genes, despite being around the same size*. So chromosome 19 is a lot more active than 18, many more proteins are being made from its much larger number of genes.
It has been known for a long time that the chromosomes are not uniformly distributed in the nucleus. The active ones, the ones like chromosome 19 with many genes, tend to be nearer the centre, while the quieter ones are near the edge. You can see this in image and schematic at top left, the less active chromosome 18 is at the bottom near the right end, while the more active chromosome 19 is above it and so away from the edge. The image is a from a paper by Bolzer et al.