1. Coordinate(坐标) data for GIS

real coordinate system:Cartesian coordinate systems(笛卡尔坐标系)

from 3D to 2D, the earth can be modled as a sphere(球体), oblate ellipsoid(扁椭圆体), geoid(大地水准面). We need a cartographic projection(地球投影)，a datum(基准面) to do this.

but there always a trade off

2. datum

a. the first national horizontal datum: Australian Geodetic Datum (AGD66) in 1966

b. new Geocentric Datum of Australia 1994 (GDA94)

c. a new one is gonna coming in 2020

#Converting between projections: transform data to a common cartographic projection

3. GDA94

units:metre

UTM projection

north+east:等角横轴割圆柱投影，圆柱投影是将一个圆柱面包围椭球体，并使之相切或相割，再根据某种条件将椭球面上的经纬网点投影到圆柱面上，然后，沿圆柱面的一条母线切开，将其展成平面而得到的投影。其中正轴圆柱投影的圆柱轴同地轴重合，横轴圆柱投影的圆柱轴同赤道直径重合，斜轴圆柱投影的圆柱轴同地轴和赤道直径以外的任一直径重合。

false easting(东伪偏移): 投影平面中为避免横轴(经度方向)坐标出现负值,而所加的偏移量

false northing(北伪偏移): 投影平面中为避免纵轴(纬度方向)坐标出现负值,而所加的偏移量

4. GLONASS: 全球导航卫星系统, used to know location without gps

5. metadata

data quality can not be changed from general to specialize, but otherwise is fine. for example, if we got the data quality of a 30*30, we do not know the data quality of a 5*5, but otherwise we will know the data quality of 30*30 if we know the data quality of 5*5

6. data dictionary简单记录了我们所需要的数据，但不是所有信息(在该地点考察并记录，可能包含一些估计值)

metadata包含了如何制作数据(如何制造这个地图)

7. meta data standard: ISO

8. spatial information: triangulation or gridding