1830 Map of Land Cover and Cultural Features in Massachusetts

Background and Data Limitations The Massachusetts 1830 map series represents a unique data source that depicts land cover and cultural features during the historical period of widespread land clearing for agricultural. To our knowledge, Massachusetts is the only state in the US where detailed land cover information was comprehensively mapped at such an early date. As a result, these maps provide unusual insight into land cover and cultural patterns in 19th century New England. However, as with any historical data, the limitations and appropriate uses of these data must be recognized: (1) These maps were originally developed by many different surveyors across the state, with varying levels of effort and accuracy. (2) It is apparent that original mapping did not follow consistent surveying or drafting protocols; for instance, no consistent minimum mapping unit was identified or used by different surveyors; as a result, whereas some maps depict only large forest blocks, others also depict small wooded areas, suggesting that numerous smaller woodlands may have gone unmapped in many towns. Surveyors also were apparently not consistent in what they mapped as ‘woodlands’: comparison with independently collected tax valuation data from the same time period indicates substantial lack of consistency among towns in the relative amounts of ‘woodlands’, ‘unimproved’ lands, and ‘unimproveable’ lands that were mapped as ‘woodlands’ on the 1830 maps. In some instances, the lack of consistent mapping protocols resulted in substantially different patterns of forest cover being depicted on maps from adjoining towns that may in fact have had relatively similar forest patterns or in woodlands that ‘end’ at a town boundary. (3) The degree to which these maps represent approximations of ‘primary’ woodlands (i.e., areas that were never cleared for agriculture during the historical period, but were generally logged for wood products) varies considerably from town to town, depending on whether agricultural land clearing peaked prior to, during, or substantially after 1830. (4) Despite our efforts to accurately geo-reference and digitize these maps, a variety of additional sources of error were introduced in converting the mapped information to electronic data files (see detailed methods below). Thus, we urge considerable caution in interpreting these maps. Despite these limitations, the 1830 maps present an incredible wealth of information about land cover patterns and cultural features during the early 19th century, a period that continues to exert strong influence on the natural and cultural landscapes of the region. For users without access to GIS software, the data are available for viewing at: http://harvardforest.fas.harvard.edu/research/1830instructions.html Acknowledgements Financial support for this project was provided by the BioMap Project of the Massachusetts Natural Heritage and Endangered Species Program, the National Science Foundation, and the Andrew Mellon Foundation. This project is a contribution of the Harvard Forest Long Term Ecological Research Program.

背景与数据局限性
马萨诸塞州1830年地图集（Massachusetts 1830 Map Series）是一类独特的数据资源，详实记录了以大规模农业开垦为主要历史特征时期的土地覆盖（land cover）与人文景观要素（cultural features）。据现有研究所知，美国境内唯有马萨诸塞州在如此早的历史阶段就完成了详尽土地覆盖信息的全域测绘。因此，这批地图为探析19世纪新英格兰地区的土地覆盖与人文格局提供了独特的研究视角。

然而，与所有历史数据一样，使用这批数据前需充分认知其局限性与合理应用场景：
（1）本批地图最初由全州各地多名测量员独立绘制，各作业团队的投入程度与测绘精度参差不齐。
（2）原始测绘未遵循统一的测绘与制图规范，具体表现为：不同测量员未统一采用最小制图单元标准。部分地图仅标注大型连片林区，其余地图则同时标注小型林木斑块，这意味着诸多城镇内的小型林地大概率未被纳入测绘范围。此外，测量员对“林地”的界定标准亦不统一：将同期独立采集的税收评估数据与这批1830年地图比对后发现，不同城镇在“林地”“未垦地”以及被标注为“林地”的“不宜垦殖土地”的相对占比上存在显著差异。部分案例中，因未遵循统一制图规范，相邻城镇的地图所呈现的森林覆盖格局差异悬殊，但两地实际的森林格局可能较为相近；甚至出现林地边界与城镇行政边界完全重合的情况。
（3）这批地图对原生林地（primary woodlands）的还原程度存在显著的城镇差异：原生林地指历史时期从未因农业开垦被破坏，但通常会被采伐以获取木材的区域，其还原程度取决于该区域农业开垦的峰值是出现于1830年之前、期间还是之后。
（4）尽管团队已尽力对这批地图进行精准地理配准（geo-reference）与数字化（digitize）处理，但在将纸质地图信息转换为电子数据文件的过程中仍引入了多种额外误差（详见下文研究方法）。

因此，我们提醒使用者在解读这批地图时需保持高度审慎。尽管存在上述局限性，1830年地图集仍蕴藏着极为丰富的19世纪早期土地覆盖格局与人文景观要素信息，而该时期至今仍对该区域的自然与人文景观有着深刻影响。对于无法访问地理信息系统（Geographic Information System, GIS）软件的使用者，可通过以下链接查看这批数据：http://harvardforest.fas.harvard.edu/research/1830instructions.html

致谢
本项目的资金支持来自马萨诸塞州自然遗产与濒危物种项目旗下的BioMap计划、美国国家科学基金会以及安德鲁·梅隆基金会。本项目为哈佛大学森林长期生态研究计划的成果之一。