名词解释
- metadata is data about the data. Usually metadata includes items such as the data of capture into digital format, data ownership, and the scale of the original map product. Metadata is crucial in establishing the appropriateness of a dataset to an analysis.
- Error is the measured difference between a true value and the value in a dataset.
- Accuracy refers to the amount of distortion from the true value
- Error propagation: the process whereby the combining of input data with error leads to error in the outputs
- Precision refers to the variation among repeated measurements and also to the amount of detail in the reporting of a measurement
- Resampling , a technique for transforming a raster image from one particular scale and projection to another
- Join, to connect two or more separately digitized maps (v) The junction between two such maps, sometimes visible as a result of imperfections in the data
8. Interpolation: this process uses known data values to predict values for unknown(unsampled) locations. Interpolation is often used with point data to create a surface of values
9. Model: a model is a representation of a real-world object or process
10. data modelling: in GIS this term refers to the way in which data can be used to predict or explain a spatially based process. A model may be a simple collection of any basic GIS functionality, such as a buffer process followed by an overlay, or it may be a highly developed, detailed approximation of reality, such as a greenhouse gas depletion model
11. raster data: data in a raster structure are cell-based data. The raster world is viewed as a surface of equally sized and spaced grid cells. Each cell contains an attribute that is generally representative of the feature occupying the majority of the cell. Examples of GIS data that are ideally treated as raster data are imagery and continuous data
12. projection: projection is an accepted mathematical process by which spatial data, which are part of the sphere of the earth, are approximated into a 2D data array. Any projection from a sphere into a flat 2D display will involve some distortion of reality. The manner in which the data are distorted depends largely on the type of projection used. A map description of the conversion of spatial data from a sphere to 2D.
13. Root Mean Square Error (RMSE) is the standard deviation of the residuals (prediction errors). Residuals are a measure of how far from the regression line data points are; RMSE is a measure of how spread out these residuals are. In other words, it tells you how concentrated the data is around the line of best fit.
14. Coordinate system: a geometric system which defines a point numerically according to an established referencing structure for the two or three dimensions of space.
Review about labs—IDW DEM
- Define the coordinate systems: Define projection tool, using when already know what the coordinate system is for a data set
- Project into a common coordinate system: Project tool
- Clip the data set so it covers only the area we will keep working on, Clip tool
- Set the environment: here including processing extent and cell size
- Feature Vertices To Points tool: Creates a feature class containing points generated from specified vertices or locations of the input features
- Interpolation
- Flow direction--flow accumulation计算集中流量，判断脊线
- Con tool will perform a conditional if/else, and get the output value based on whether the cell value is matching with specified conditional statement
Review the labs—ANUDEM
- Topo to Raster tool, tell the system what each file represents and which field to use
- To compare IDW and ANUDEM together, using minus tool, add the coastlines inside and compare them together
Slope
1. the slope tool identifies the steepness at each cell of a raster surface. the lower the slope value, the flatter the terrain; the higher the slope value, the steeper the terrain坡度值越低，地形越平坦，坡度值越高，地形越陡峭
Aspect
1. identifies the direction the downhill slope faces测量下坡坡面的方向
Data Structure
the data structure refers to the manner in which GIS allows storage and display of spatial information, the most common structures are vector and raster.
vector data:
1. analysed as polygons, lines or points. The user's choice of the correct geographical promitive to represent data will depend on scale, or the level of generalisation in the data called multiple representation problem. 举例来讲在一个small-scale map上一个城市可以又一个point表示，在另一个比例尺下可能需要用polygon表示
2. vector GIS is more accurate than raster GIS in defining spatial location, although it is generally more expensive in terms of data storage and computing power
3. able to support topology explicitly.
raster data
1. easier to store and use data
2. compatible with remotely sensed imagery与遥感图像兼容，and any feature that varies rather than discrete data数据是连续的而非离散的
3. does not support topology explicitly