A method of storing data indicating a property of a communications network, the method comprising: obtaining a stored data item associated with at least part of a spatial region and having an associated spatial parameter and an associated temporal parameter, the stored data item indicating a property of the communications network; receiving second data indicating a property of said communications network at a particular location in said spatial region at a particular time; and processing said spatial parameter, said temporal parameter, data indicating said particular location and data indicating said particular time and, based upon said processing, generating first and second sub-data items (D20, D21), each of said first and second sub-data items having an associated spatial parameter (22A, 22B) and an associated temporal parameter, at least one of the first and second sub-data items having a spatial or temporal parameter different from that associated with the stored data item, wherein said generating said first and second sub-data items comprises: determining a spatial relationship between said spatial parameter and data indicating said particular location; determining a temporal relationship between said temporal parameter and data indicating said particular time; and generating said first and second sub-data items if at least one of said determined spatial relationship and determined temporal relationship satisfy a respective predetermined spatial or temporal criterion. obtaining a stored data item associated with at least part of a spatial region and having an associated spatial parameter and an associated temporal parameter, the stored data item indicating a property of the communications network; receiving second data indicating a property of said communications network at a particular location in said spatial region at a particular time; and processing said spatial parameter, said temporal parameter, data indicating said particular location and data indicating said particular time and, based upon said processing, generating first and second sub-data items (D20, D21), each of said first and second sub-data items having an associated spatial parameter (22A, 22B) and an associated temporal parameter, at least one of the first and second sub-data items having a spatial or temporal parameter different from that associated with the stored data item, wherein said generating said first and second sub-data items comprises: determining a spatial relationship between said spatial parameter and data indicating said particular location; determining a temporal relationship between said temporal parameter and data indicating said particular time; and generating said first and second sub-data items if at least one of said determined spatial relationship and determined temporal relationship satisfy a respective predetermined spatial or temporal criterion. determining a spatial relationship between said spatial parameter and data indicating said particular location; determining a temporal relationship between said temporal parameter and data indicating said particular time; and generating said first and second sub-data items if at least one of said determined spatial relationship and determined temporal relationship satisfy a respective predetermined spatial or temporal criterion.