| Keyword | CPC | PCC | Volume | Score |
|---|---|---|---|---|
| metro system in the world | 1.58 | 0.9 | 4832 | 81 |
| world's largest metro system | 0.87 | 0.7 | 2163 | 49 |
| world's longest metro system | 1.19 | 0.2 | 3211 | 78 |
| top 10 largest metro system in the world | 1.31 | 0.5 | 2850 | 82 |
| biggest metro system in the world | 0.88 | 0.6 | 2988 | 60 |
| world's first metro system | 1.71 | 0.2 | 8488 | 35 |
| oldest metro system in the world | 0.14 | 0.3 | 9335 | 53 |
| smallest metro system in the world | 1.24 | 1 | 4602 | 88 |
| longest metro system in the world | 1.54 | 0.6 | 8822 | 56 |
| world's biggest metro system | 0.05 | 0.1 | 388 | 30 |
| largest metro in the world | 0.04 | 0.8 | 9253 | 42 |
| biggest metro in the world | 1.88 | 1 | 4419 | 5 |
| largest metro systems in us | 1.18 | 0.9 | 510 | 74 |
| busiest metro systems in the world | 1.47 | 0.3 | 7428 | 84 |
| top metro systems in the world | 1.99 | 0.2 | 9737 | 54 |
| largest metro areas in the world wikipedia | 0.45 | 0.7 | 567 | 33 |
| largest metro areas in the world | 1.4 | 0.5 | 4185 | 5 |
| biggest metro areas in the world | 0.31 | 0.4 | 988 | 25 |
