1. EIA regions
States are grouped by the nine standard geographic divisions — the Census divisions — that the U.S. Energy Information Administration uses.
The map shows the nine divisions, and which states belong to them.
New England
Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont
Middle Atlantic
New Jersey, New York, Pennsylvania
East North Central
Illinois, Indiana, Michigan, Ohio, Wisconsin
West North Central
Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota
South Atlantic
Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia
East South Central
Alabama, Kentucky, Mississippi, Tennessee
West South Central
Arkansas, Louisiana, Oklahoma, Texas
Mountain
Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming
Pacific
Alaska, California, Hawaii, Oregon, Washington
2. RTO / ISO regions
States are grouped based on which Regional Transmission Organization or Independent System Operator runs the wholesale electricity market. There are also two large non-RTO blocks — the West and the South — where states are not part of an organized market. These groupings give us insight into electricity markets and grid operations.
RTO or ISO territories do not follow state lines exactly — a single state can have load served by more than one market. To keep whole states comparable across every chart, we assign each state to the region that serves the majority of its retail electricity load, based on balancing-authority data reported in the EIA's Form 861.
Every assigned state has a majority of its load served by that region, and most are well clear of the line — South Dakota is the narrowest at 50.9% (SPP), followed by New Mexico at 54.5% and North Dakota at 55.0%. States that are majority-served by utilities outside of RTOs are grouped into Non-RTO West and Non-RTO South. Alaska and Hawaii are not connected to any interconnection and form their own small Off-grid group.
The state of Missouri is the exception. Its load is split almost evenly across two RTOs (MISO and SPP) and non-RTO utilities, without a clear majority. Rather than assign it arbitrarily, Missouri is not assigned to any region.
PJM · PJM Interconnection
Delaware, District of Columbia, Illinois, Maryland, New Jersey, Ohio, Pennsylvania, Virginia, West Virginia
MISO · Midcontinent ISO
Arkansas, Indiana, Iowa, Louisiana, Michigan, Minnesota, Wisconsin
SPP · Southwest Power Pool
Kansas, Nebraska, North Dakota, Oklahoma, South Dakota
ERCOT · Electric Reliability Council of Texas
Texas
CAISO · California ISO
California
ISO-NE · ISO New England
Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont
NYISO · New York ISO
New York
Non-RTO West
Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming
Non-RTO South
Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee
Off-grid
Alaska, Hawaii
Not assigned
Missouri — its load is split across MISO, SPP and non-RTO utilities with no majority
How regional values are calculated
It depends on the type of metric:
Totals such as electricity generation, capacity, or consumption — are calculated by summing the values of every member states.
Rates and averages —such as prices, per-capita values, carbon intensity, or shares — are a weighted average of the member states. For example, retail electricity prices are weighted by each state's electricity sales and per-capita figures by population. This means a region's price or intensity gives more weight to larger states, rather than weighing small and large states equally.