qdgc Venezuela

QDGC tables delivered in geopackage file
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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.

Within each geopackage file you will find a number of tables with these names:
-tbl_qdgc_01
-tbl_qdgc_02
-tbl_qdgc_03
-tbl_qdgc_04
-tbl_qdgc_05
-etc

The attributes for each table are:
qdgc Unique Quarter Degree Grid Cell reference string
level_qdgc QDGC level
cellsize degrees decimal degree for the longitudal and latitudal length of the cell
lon_center Longitude center of the cell
lat_center Latitudal center of the cell
area_km2 Calculated area for the cell
geom Geometry

Metadata
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Geodata GCS_WGS_1984
Datum: D_WGS_1984
Prime Meridian: 0

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:
- st_area(st_transform(geom, 102022))/1000000)

Conditions
----------
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

Thankyou!
--------
The work has over the years been supported and received advice and moral support from many organisations and stakeholders. Here are some of them:
- TAWIRI (http://tawiri.or.tz/)
- Dept of Biology, NTNU, Norway
- Norwegian Environment Agency
- Eivin Røskaft, Steven Prager, Howard Frederick, Julian Blanc, Honori Maliti, Paul Ramsey

References
----------
* 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

以地理数据包（Geopackage）格式交付的QDGC数据表
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QDGC（四分度网格系统）是一种通过生成近似等面积正方形网格覆盖特定区域，以表征该区域特定属性的方法。该网格单元基于全球经纬度方格划分：赤道方向共有360条经线，南北极方向共有180条纬线，二者组合可得到覆盖全球的64800个网格分片或瓦片。

每个地理数据包文件中均包含若干数据表，命名格式如下：
- tbl_qdgc_01
- tbl_qdgc_02
- tbl_qdgc_03
- tbl_qdgc_04
- tbl_qdgc_05
- 以此类推

每张数据表包含以下字段：
qdgc：唯一四分度网格单元标识字符串
level_qdgc：QDGC层级
cellsize：单元格经向与纬向长度的十进制度数
lon_center：单元格中心经度
lat_center：单元格中心纬度
area_km2：单元格计算得到的面积（单位：平方千米）
geom：几何图形

元数据
--------
地理坐标系统：GCS_WGS_1984
基准面：D_WGS_1984
本初子午线：0°

面积计算采用不同版本的阿尔伯斯等面积圆锥投影，通过PostGIS的st_area函数实现。针对非洲大陆，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

使用条款
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本数据集按现状交付，不提供任何担保。若发现错误，请告知我，我将尽力修正。相关改进建议可提交至该GitHub仓库：https://github.com/ragnvald/qdgc

致谢
--------
本项目多年来获得了众多机构与相关方的支持、建议与精神鼓励，部分支持方与贡献者如下：
- TAWIRI（http://tawiri.or.tz/）
- 挪威科技大学生物系（Dept of Biology, NTNU, Norway）
- 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