An Improved Schema for Vector Tile Map Considering Symbol Integrity

  Objectives  Vector tile technology is considered as a new generation of Web map solution. Compared with raster tile, vector tile is more flexible. It renders the map based on vector data and preset styles on the client. Therefore, users can easily change map styles without reproducing tile data. However, in vector tile maps, the features that cross the grid are divided into multiple parts, which often cause non-uniform symbol discontinuities of point, line, and area features. It not only affects visualization effect, but also leads to spatial cognitive errors.

  Methods  On the premise of independence coordinate data and symbol style of vector tile, a schema combining preprocessing and real-time rendering is proposed to solve these problems. By analyzing the types and causes of discontinuity of different feature's symbols at the grid boundary, drawing auxiliary information for different types of symbols is extracted, which is used to adjust initial position of symbol unit in the tile and to realize the continuous representation of symbols.

  Results  A prototype system based on this scheme was developed and a large scale map mapping experiment was performed. Experimental results show that the proposed method can solve the problem of symbol discontinuity at the grid boundary.

  Conclusions  The proposed method can meet the needs of vector tile production and drawing in terms of reu-sability and efficiency.