A change in how Walmart maps out its delivery routes means the service will now be available to 12 million more people, including some who may qualify for same-day-delivery for the first time.

The nation’s largest retailer announced this week it was switching to “geospatial technology” to optimize delivery zones. In the past, Walmart delivery was based on traditional boundaries like ZIP codes. Now, large areas will be divided into smaller, more precise hexagonal grids that resemble pixels in a digital image. The hexagons are linked together to cover a greater area and prevents small areas around the edges from being left out of the delivery zones.

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Different delivery elements – things like available times, drive time and store location – are available for each hexagon.

The change, Walmart said, allows it to adjust delivery zones with greater accuracy, including making it easier for items that aren’t available from one store to be delivered from another.

Here’s how Walmart explained the importance of that change.

“Customers can now have their delivery orders fulfilled by multiple Walmart stores within their service area. Previously, a customer’s order might have been fulfilled by a single Walmart store based on their location, which sometimes meant that if a product wasn’t available at that store, the customer would receive their order in multiple deliveries at different times. Now, with geospatial technology refining and expanding our delivery zones, a customer may be covered by multiple stores. If one store doesn’t have a particular item but another nearby location does, Walmart delivery drivers can pick up products from both, ensuring customers receive everything they need in one seamless delivery.”

The change opens up delivery to 12 million more households, including an expansion of same-day delivery.