Spark Shipping pulls your multi-locations from Shopify, this list is refreshed daily. You can find it in Spark Shipping under your site settings (Navigate to Sites > Overview > Multi Location Configuration)
For accurate location inventory management, users can map each vendor in Spark Shipping to a location that they have in Shopify. Once mapped, Spark Shipping will start pushing inventory quantities from each vendor only to the mapped location.
Need help on how to set this up on the Shopify side? Visit this help article on Shopify: https://help.shopify.com/en/manual/locations