Keeping map labels consistent across multiple zoom levels

摘要

A computer server prepares application-specific map data responsive to a request from a client device. The application-specific map data includes map feature data and label data which itself includes information that specifies one or more zoom levels for which the label information is appropriate to display. When generating the label data, a type table that designates label style information by feature type and by zoom level may be used at the server. The map feature data may also include a relative rank for each feature that is passed to its corresponding label. The display order allows the map client, when generating the map, to select the most appropriate labels to display when the display of all possible labels would cause clutter or otherwise violate label display rules.

主权项

1. A method of operating a server device that provides data to a computer device, the data used on the computer device to display map data, wherein the map data includes map feature data used to draw map features and label data used for displaying text labels and symbols that identify map features, the method comprising:
receiving, at the server device, label data associated with a map feature, each map feature having a feature type; receiving, at the server device, a type table that specifies style information by feature type for label data at one or more zoom levels including, for a particular feature type corresponding to a set of labels, first label style information for a first range of zoom levels and second label style information for a second range of zoom levels, wherein style information includes at least one of: a font type, a font size, or a font color, and wherein the first label style information is different from the second label style information; receiving, at the server device via a network, a request from the computer device for map data; creating label data responsive to the request, the label data including label text, the first label style information, and the first range of zoom levels for which the label data is valid according to the particular feature type in the type table; and sending map feature data and the label data responsive to the request to the computer device for use by the computer device in displaying the map feature data and the label data, wherein when the computer device receives a new request to display the map data at a new zoom level that is outside the first range of zoom levels for which the currently displayed label data is valid, the label data causes the computer device to: receive, from the server device, new label data having a valid range that covers the new zoom level, display the map data at the new zoom level, determine that the difference between the new label data and the currently displayed label data is below a predetermined threshold difference, and retain the currently displayed label data at the new zoom level.