Electricity reaches you in three stages. Generation is where power is made — power plants and wind and solar farms. Transmission carries it long distances at very high voltage over the big steel-tower lines that cross the landscape. Distribution is the last stretch: substations step the voltage down and local lines on wooden poles carry it to your street and into your home.
Each stage can fail, but they fail at very different scales. A transmission or generation problem can darken a whole region at once and makes headlines. Those events are comparatively rare because that part of the grid is heavily monitored and built with backups.
The large majority of outages are local distribution faults — a tree limb on a neighborhood line, a blown transformer, a damaged pole. These affect a single street or town rather than a region, which is why on any outage map you usually see scattered local pockets rather than one giant blackout.
Understanding the three stages explains what you see on the map. A small, sharp-edged outage that clears in an hour is almost always a distribution fault; a large area going dark together points higher up the chain, toward transmission, generation, or a grid operator deliberately shedding load to keep the rest of the system stable.