Added the layouts used for DRC ruleset development to sky130/custom/drc/.
diff --git a/sky130/custom/drc/nsd.mag b/sky130/custom/drc/nsd.mag
new file mode 100644
index 0000000..7adb99e
--- /dev/null
+++ b/sky130/custom/drc/nsd.mag
@@ -0,0 +1,95 @@
+magic
+tech sky130A
+magscale 1 2
+timestamp 1602981775
+<< error_p >>
+rect 1389 1491 1406 1610
+rect 1469 1491 1486 1610
+rect 1807 1527 1815 1579
+rect 1851 1527 1867 1579
+rect 1998 1519 2006 1581
+rect 2057 1519 2073 1581
+rect 2487 1476 2523 1606
+rect 2567 1476 2603 1606
+rect 1878 525 1886 577
+rect 1922 525 1938 577
+rect 1443 486 1448 511
+rect 2425 491 2429 516
+rect 2732 492 2740 554
+rect 2791 492 2807 554
+rect 3471 538 3479 590
+rect 3515 538 3531 590
+<< nwell >>
+rect 1134 1328 1911 1772
+rect 1151 348 1976 792
+rect 3212 348 3748 792
+<< ndiff >>
+rect 3723 1631 3986 1742
+rect 2290 1476 2523 1606
+rect 2567 1476 2800 1606
+rect 3723 1565 3818 1631
+rect 3879 1565 3986 1631
+rect 3161 1510 3191 1540
+rect 3723 1465 3986 1565
+rect 2233 516 2404 635
+rect 3816 446 3943 692
+<< pdiff >>
+rect 1234 1491 1406 1610
+rect 1469 1491 1646 1610
+rect 1251 511 1423 630
+rect 3585 443 3712 689
+<< psubdiff >>
+rect 1998 1581 2065 1648
+rect 1998 1456 2065 1519
+rect 2523 1476 2567 1606
+rect 2404 516 2568 635
+rect 2425 453 2568 516
+rect 2732 554 2799 621
+rect 2732 429 2799 492
+rect 3053 451 3186 695
+<< nsubdiff >>
+rect 1406 1491 1469 1610
+rect 1807 1579 1859 1619
+rect 1807 1483 1859 1527
+rect 1423 511 1583 630
+rect 1443 419 1583 511
+rect 1878 577 1930 617
+rect 1878 481 1930 525
+rect 3248 446 3381 690
+rect 3471 590 3523 630
+rect 3471 494 3523 538
+<< psubdiffcont >>
+rect 1998 1519 2065 1581
+rect 2732 492 2799 554
+<< nsubdiffcont >>
+rect 1807 1527 1859 1579
+rect 1878 525 1930 577
+rect 3471 538 3523 590
+<< locali >>
+rect 1807 1579 1859 1619
+rect 1807 1483 1859 1527
+rect 1998 1581 2065 1648
+rect 1998 1456 2065 1519
+rect 1878 577 1930 617
+rect 1878 481 1930 525
+rect 2732 554 2799 621
+rect 3471 590 3523 630
+rect 3471 494 3523 538
+rect 2732 429 2799 492
+<< labels >>
+flabel comment s -23 575 -17 575 0 FreeSans 560 0 0 0 Correct_by_design
+flabel comment s 1626 2208 1626 2208 0 FreeSans 560 0 0 0 Use_cif_see_NPLUS
+flabel comment s 292 2248 292 2248 0 FreeSans 800 0 0 0 N+_Implant_(nsd)
+flabel comment s 1428 1158 1428 1158 0 FreeSans 560 0 0 0 nsd.1
+flabel comment s 2568 1235 2568 1235 0 FreeSans 560 0 0 0 nsd.2
+flabel comment s 1506 221 1506 221 0 FreeSans 560 0 0 0 nsd.5b
+flabel comment s 2405 266 2405 266 0 FreeSans 560 0 0 0 nsd.5a
+flabel comment s -39 354 -39 354 0 FreeSans 560 0 0 0 nsd.3
+flabel comment s -19 185 -19 185 0 FreeSans 560 0 0 0 nsd.6
+flabel comment s 3560 266 3560 266 0 FreeSans 560 0 0 0 nsd.7
+flabel comment s 3291 1779 3297 1779 0 FreeSans 560 0 0 0 Incorrect
+flabel comment s 3245 1364 3245 1364 0 FreeSans 560 0 0 0 nsd.10a
+flabel comment s 3862 1342 3862 1342 0 FreeSans 560 0 0 0 nsd.11
+flabel comment s -11 -81 -11 -81 0 FreeSans 560 0 0 0 nsd.9
+flabel comment s 15 48 15 48 0 FreeSans 560 0 0 0 nsd.8
+<< end >>
