Progressive spatial searching using augmented structures

A method comprising:

• generating a character string search structure that includes an initial node and a plurality of internal nodes included in string paths from the initial node to terminal nodes, each string path representing a valid character string;
• storing at least one retrieval item in a computing device storage area associated with each terminal node, wherein the retrieval item includes an item location indicator and a recommendation indicator associated with the retrieval item;
• determining a cardinality of augmented non-terminal nodes for storing spatial bound indicators indicating bounds of sub-structures of the character string search structure that emanate from the augmented non-terminal nodes;
• determining a set of augmented non-terminal nodes based on comparing a benefit value of each augmented non-terminal node with a benefit value of an ancestor node of the augmented non-terminal node in the character string search structure, based on a benefit function of nodes and having the determined cardinality;
• determining spatial bound values associated with spatial regions represented by each of the augmented non-terminal nodes included in the set, based on comparing error values of bounds associated with a first non-terminal node spatial region with error values of bounds associated with spatial regions associated with nodes that are descendants of the first non-terminal node;
• and
• storing each spatial bound value in association with the respective associated augmented non-terminal node.