Micro controller manufactures have lots of knowledge & techniques than us & we are still in the beginning stage. The new technology comes faster than our learning curve.
To program a PIC there must be minimum five wires coming from the programmer to the target board they are
*VPP/MCLR
*VDD (Target)
*VSS (GND)
*ICSPDAT/PGD
*ICSPCLK/PGC
If you go through these pins in the PICs they are placed in the same position on each device pin package.
Ex
For all 18 pin PICs the above pins are located on the same position.
For all 8 pin PICs the above pins are located on the same position.
For all 40 pin PICs the above pins are located on the same position.
Why the above program pins are located in the same position?
Because from a one target socket you can program different size PICs.
So you must place the package (PIC) in the correct position shows in your diagram, so only the programming pins will contact with the programmer.
If the manufacture placed the programming pins on different locations then how can the programmer identify where the programming pins are?
That’s why they have manufactured according to a standard.