Yosemite National Park - Burn Frequency - Open Data

Fire history taken from historic records kept at Yosemite National Park. Fires in more recent years were recorded from fire perimeters drawn on paper maps and/or recorded by GPS Unit. Original data was interpreted from historical fire records held at Yosemite National Park in the late 1980s. Polygons depicting burned areas were drawn on 1:62,500 USGS maps (15" series) based on written descriptions in the fire records. Fires less than 10 acres in size were depicted as points. Mylar film was placed over paper maps and registered with tic marks at map corners. Fires were traced on Mylar and sent to a contractor for digitizing into SAGIS vector format. Fires depicted as points were given the area noted in the fire records by buffering the points. SAGIS data was converted to GRASS format when Yosemite migrated to GRASS. GRASS data was converted to Arc/Info coverage format when Yosemite migrated to Arc/Info in 1995. Some vector data was lost in conversion from GRASS. In those instances, polygons were vectorized from raster versions that remained in GRASS. Each year from 1995 - 2000, fires were input into Arc/Info by digitizing 1:24,000 USGS paper maps (7.5" series) or from Trimble GPS readings. Starting 2001, all larger fire perimeters were acquired through ground GPS or helicopter GPS reconnaissance. Small fire point locations were acquired through ground GPS or helicopter GPS and buffered to approximate fire size. IRMA Data Store Reference本数据集的火灾历史数据源自优胜美地国家公园（Yosemite National Park）留存的历史档案。近年的火灾记录通过纸质地图绘制的火灾边界或GPS设备记录获取。原始数据于20世纪80年代末从优胜美地国家公园的历史火灾档案中整理解读而来。研究人员依据火灾档案中的文字描述，在1:62500比例尺的美国地质调查局（USGS）15分幅系列纸质地图上绘制了表征过火区域的多边形。面积小于10英亩的火灾以点要素形式标注。将聚酯薄膜（Mylar film）覆盖于纸质地图之上，并通过地图四角的刻度标记完成配准。研究人员在聚酯薄膜上描摹火灾范围，并将其交付承包商，以SAGIS矢量格式进行数字化处理。以点要素标注的火灾，通过对点要素进行缓冲区分析，赋予火灾档案中记录的面积数值。当优胜美地国家公园迁移至GRASS地理信息系统平台时，原SAGIS格式数据被转换为GRASS格式；1995年该机构迁移至Arc/Info平台时，GRASS格式数据又被转换为Arc/Info Coverage格式。部分矢量数据在GRASS格式转换过程中丢失，对此类情况，研究人员通过GRASS中留存的栅格版本重新矢量化得到多边形要素。1995年至2000年间，每年的火灾数据均通过数字化1:24000比例尺的美国地质调查局（USGS）7.5分幅系列纸质地图，或通过Trimble GPS读数录入Arc/Info系统。2001年起，所有大型火灾边界均通过地面GPS或直升机GPS勘察获取；小型火灾的点位信息通过地面或直升机GPS获取，并通过缓冲区分析得到近似过火面积。数据引用：IRMA Data Store Reference