Yosemite National Park - Fire History - 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本火灾历史数据集源自约塞米蒂国家公园（Yosemite National Park）留存的历史火灾记录。其中，早期原始数据于20世纪80年代末从该公园的历史火灾档案中解读得到：基于火灾记录中的文字描述，研究人员在1:62500比例尺的美国地质调查局（United States Geological Survey, USGS）15分幅系列纸质地图上绘制了表征过火区域的多边形要素，面积小于10英亩的火灾则以点要素进行表征。近年的火灾数据则通过两种方式采集：一是从纸质地图上绘制的火灾边界获取，二是借助GPS设备（GPS Unit）直接记录。具体流程为：将聚酯薄膜（Mylar film）覆盖于纸质地图之上，通过地图四角的十字标记完成配准后，将火灾边界描绘于聚酯薄膜上，随后交由承包商将其数字化为SAGIS矢量格式。对于以点要素表征的小型火灾，通过对点进行缓冲区分析，赋予其火灾记录中记载的实际过火面积。当约塞米蒂国家公园升级至GRASS地理信息系统时，SAGIS格式的数据被转换为GRASS格式；1995年该公园迁移至Arc/Info系统时，GRASS格式的数据进一步被转换为Arc/Info Coverage格式。部分矢量数据在GRASS格式的转换过程中发生丢失，此类情况下，研究人员从GRASS系统中留存的栅格版本数据中矢量化提取得到多边形要素。1995年至2000年期间，每年的火灾数据均通过两种方式录入Arc/Info系统：一是数字化1:24000比例尺的美国地质调查局（USGS）7.5分幅系列纸质地图，二是借助天宝（Trimble）GPS观测数据直接录入。2001年起，所有大型火灾的边界均通过地面GPS或直升机搭载GPS侦察获取；小型火灾的点位信息通过地面GPS或直升机搭载GPS采集，并通过缓冲区分析得到近似的过火面积。IRMA数据存储引用