qdgc Nigeria
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QDGC tables delivered in geopackage file<br> - - - - - - - - - - - - - - - - - - - - - -<br> QDGC represents a way of making (almost) equal area squares covering a specific area to represent specific qualities of the area covered. The squares themselves are based on the degree squares covering earth. Around the equator we have 360 longitudinal lines , and from the north to the south pole we have 180 latitudinal lines. Together this gives us 64800 segments or tiles covering earth.<br> <br> <br> <br> <br> Within each geopackage file you will find a number of tables with these names:<br> <br> <br> <br> <br> -tbl_qdgc_01<br> -tbl_qdgc_02<br> -tbl_qdgc_03<br> -tbl_qdgc_04<br> -tbl_qdgc_05<br> -etc<br> <br> <br> <br> <br> The attributes for each table are:<br> <br> <br> <br> <br> qdgc Unique Quarter Degree Grid Cell reference string<br> area_reference Country<br> level_qdgc QDGC level<br> cellsize degrees decimal degree for the longitudal and latitudal length of the cell<br> lon_center Longitude center of the cell<br> lat_center Latitudal center of the cell<br> area_km2 Calculated area for the cell<br> geom Geometry<br> <br> <br> <br> <br> Metadata<br> --------<br> Geodata GCS_WGS_1984<br> Datum: D_WGS_1984<br> Prime Meridian: 0<br> <br> <br> <br> <br> Areas are calculated with different versions of Albers Equal Area Conic using the PostGIS function st_area. For the African continent I have used Africa Albers Equal Area Conic which will look like this:<br> - st_area(st_transform(geom, 102022))/1000000)<br> <br> <br> <br> <br> Licensing<br> ---------<br> Creative Commons Attribution 4.0 International<br> <br> <br> <br> <br> Conditions<br> ----------<br> Delivered to the user as-is. No guarantees. If you find errors, please tell me and I will try to fix it. Suggestions for improvements can be addressed to the github repository: https://github.com/ragnvald/qdgc<br> <br> <br> <br> <br> Thankyou<br> --------<br> The work has over the years been supported and received advice and moral support from many organisations and stakeholders. Here are some of them:<br> - Tanzania Wildlife Research Institute<br> - Dept of Biology, NTNU, Norway<br> - Norwegian Environment Agency<br> - Eivin Røskaft, Steven Prager, Howard Frederick, Julian Blanc, Honori Maliti, Paul Ramsey<br> <br> <br> <br> <br> References<br> ----------<br> * http://en.wikipedia.org/wiki/QDGC<br> * http://www.mindland.com/wp/projects/quarter-degree-grid-cells/about-qdgc/<br> * http://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection<br> * http://www.safe.com<br> <br> <br> <br> <br> <br> <br> <br> <br> Ragnvald Larsen<br> Trondheim 21th of January, 2021<br> <br> <br> <br> <br> ragnvald@mindland.com<br> www.mindland.com
以地理包（Geopackage）文件形式交付的QDGC表格 ---------------------------------------- QDGC（Quarter Degree Grid Cell，四分之一度数格网单元）是一种通过覆盖特定区域的近似等面积正方形来表征该区域特定属性的方法。此类正方形基于覆盖地球的度数方格构建：沿赤道方向共有360条经线，南北极方向共有180条纬线，二者共同构成了覆盖全球的64800个分段或格网瓦片。 每个地理包文件中均包含以下命名格式的表格： - tbl_qdgc_01 - tbl_qdgc_02 - tbl_qdgc_03 - tbl_qdgc_04 - tbl_qdgc_05 - 以此类推 各表格的属性字段如下： qdgc：唯一四分之一度数格网单元引用字符串 area_reference：所属国家/地区 level_qdgc：QDGC层级 cellsize：格网单元经向与纬向长度的十进制度数 lon_center：格网单元中心点经度 lat_center：格网单元中心点纬度 area_km2：格网单元计算面积（单位：平方千米） geom：几何图形（Geometry） 元数据 -------- 地理数据坐标系：GCS_WGS_1984 基准面：D_WGS_1984 本初子午线：0° 格网面积采用PostGIS的st_area函数结合多种阿尔伯斯等面积圆锥投影（Albers Equal Area Conic）进行计算。针对非洲大陆，本数据集使用非洲阿尔伯斯等面积圆锥投影，计算表达式如下： `st_area(st_transform(geom, 102022))/1000000` 授权协议 --------- 知识共享署名4.0国际许可协议（Creative Commons Attribution 4.0 International） 使用条款 ---------- 本数据集按现状提供，不附带任何形式的保证。若发现数据错误，请告知作者，作者将尽力修正。相关改进建议可提交至GitHub仓库：https://github.com/ragnvald/qdgc 致谢 -------- 本数据集的制作多年来得到了众多机构与相关方的支持、建议与精神鼓励，在此一并致谢，部分支持方名单如下： - 坦桑尼亚野生动物研究所 - 挪威科技大学生物系 - 挪威环境局 - Eivin Røskaft、Steven Prager、Howard Frederick、Julian Blanc、Honori Maliti、Paul Ramsey 参考文献 ---------- * http://en.wikipedia.org/wiki/QDGC * http://www.mindland.com/wp/projects/quarter-degree-grid-cells/about-qdgc/ * http://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection * http://www.safe.com 作者：Ragnvald Larsen 特隆赫姆，2021年1月21日 邮箱：ragnvald@mindland.com 官网：www.mindland.com
