Tiled vector data model for the geographical features of symbolized maps

Electronic maps (E-maps) provide people with convenience in real-world space. Although web map services can display maps on screens, a more important function is their ability to access geographical features. An E-map that is based on raster tiles is inferior to vector tiles in terms of interactive ability because vector maps provide a convenient and effective method to access and manipulate web map features. However, the critical issue regarding rendering tiled vector maps is that geographical features that are rendered in the form of map symbols via vector tiles may cause visual discontinuities, such as graphic conflicts and losses of data around the borders of tiles, which likely represent the main obstacles to exploring vector map tiles on the web. This paper proposes a tiled vector data model for geographical features in symbolized maps that considers the relationships among geographical features, symbol representations and map renderings. This model presents a method to tailor geographical features in terms of map symbols and ‘addition’ (join) operations on the following two levels: geographical features and map features. Thus, these maps can resolve the visual discontinuity problem based on the proposed model without weakening the interactivity of vector maps. The proposed model is validated by two map data sets, and the results demonstrate that the rendered (symbolized) web maps present smooth visual continuity.

电子地图（Electronic maps，简称E-maps）为人们在现实空间中提供了诸多便利。尽管网络地图服务能够在屏幕上展示地图，但其更为核心的功能在于可访问地理要素。基于栅格瓦片（raster tiles）的电子地图在交互性能上劣于基于矢量瓦片（vector tiles）的电子地图，这是因为矢量地图为访问和操作网络地图要素提供了便捷高效的途径。然而，瓦片式矢量地图渲染面临的关键问题在于：通过矢量瓦片以地图符号（map symbols）形式渲染的地理要素，可能会引发视觉不连续性（visual discontinuities）问题，例如瓦片边界周边出现图形冲突（graphic conflicts）与数据丢失（data loss），这大概率成为网络端矢量地图瓦片探索应用的主要障碍。本文针对符号化地图（symbolized maps）中的地理要素提出了一种瓦片矢量数据模型（tiled vector data model），该模型充分考量了地理要素、符号表达与地图渲染（map renderings）三者之间的关联关系。该模型提出了一种基于地图符号适配地理要素的方法，并在地理要素与地图要素两个层级上实施“拼接（连接）”操作。基于该模型，此类地图可在不削弱矢量地图交互性能的前提下，解决视觉不连续性问题。本文提出的模型通过两组地图数据集进行了验证，结果表明，渲染（符号化）后的网络地图可实现平滑的视觉连续性。