TA Tutorial in Spring Semester 2015

GRID-BASED ANALYSIS IN GIS

Prof. Yuji Murayama - Instructor Hao HOU – Teaching Assistant Division of Spatial Information Science University of Tsukuba

Definition of Grid in Cartography

 In cartography, any network of parallel and perpendicular lines superimposed on a map and used for reference. These grids are usually referred to by the map projection or coordinate system they represent (Esri, 2015).  A spatial grid refers to a two-dimensional grid system that spans a feature class. It is used to quickly locate features in a feature class that might match the criteria of a spatial search (Esri, 2015). (http://wattsupwiththat.com/2012/04/09/shakun-not-stirred-and-definitely-not-area-weighted/)

Definition of Grid in GIS

 An data format for storing raster data as well as summering vector data that defines geographic space as an array of equally sized square cells arranged in rows and columns. Each cell stores a numeric value that represents a geographic for that unit of space. Each grid cell is referenced by its x,y coordinate location (Esri, 2015). (http://wattsupwiththat.com/2012/04/09/shakun-not-stirred-and-definitely-not-area-weighted/)

Introduction to Grid-based Analysis

Grid Mesh  Grid-based analysis is a method for arranging data into a specific unit.

 The size of each grid is defined by users and normally it is determined according to purpose, scale or the available data format.

 Grid-based analysis offers a way to combine vector data with raster data.

 There are two types of grids: integer and floating point. Use integer grids to represent discrete data and floating-point grids to represent continuous data (Esri, 2015). Grid Map

Discrete Data

 Discrete data, which is sometimes called thematic, categorical, or discontinuous data, most often represents objects in both the feature (vector) and raster data storage systems. A discrete object has known and definable boundaries: it is easy to define precisely where the object begins and where it ends.  Examples of discrete data: Point: park, bus stop, road intersection… Line: road, river, airline… Polygon: different types of land use and land cover

Continuous Data

 A continuous surface represents phenomena in which each location on the surface is a measure of the concentration level or its relationship from a fixed point in space or from an emitting source.  Definition of grid’s value: 1. Fixed phenomena: concentration level or its relationship from a fixed point in space or from an emitting source. 2. Varied phenomena: type or manner in which the phenomenon moves.

(http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000007000000)

Advantage

 Create standard data format for further study.

 Combine vector data with raster data.

 Conclude data in a big area for spatial understanding.

Grid-based Analysis

Grid-based Analysis Cases

 Case study of urban land use (Bagan, H., & Yamagata, Y. 2012. Landsat analysis of urban growth: How Tokyo became the world's largest megacity during the last 40 years.) 1. Integrate remote sensing, GIS, and statistical data within the cells; 2. Quantify land-cover changes in terms of the percentage of area affected and rates of change and compare them with population census data; 3. Analyze the spatial-temporal dynamics of urban growth patterns.

(Percentage change of urban/built-up area in 1-km2 grid cells from 1972 to 2011)

Grid-based Analysis Cases

 Case study of hazard (Su, M. D., Kang, J. L., Chang, L. F., & Chen, A. S. 2005. A grid-based GIS approach to regional flood damage assessment.) Work Flow Flood hazard map from computer modeling

Grid-based Analysis Cases

 Case study of environmental protection (Richards, M., Ghanem, M., Osmond, M., Guo, Y., & Hassard, J. 2006. Grid-based analysis of air pollution data.) 1. Deploy a sensor network over a target region, such as a heavily industrialized or densely populated area ; 2. Create a wealth of data allowing new types of analyses to be conducted; 3. Analyze and visualize spatiotemporal variation of multiple pollutants with respect to one another, and their correlation with third-party data.

(Interpolated color pollution representation over vector map layers)

Grid-based Analysis of Raster Data in ArcGIS

Compare two raster shape files in different spatial resolutions 30m × 30m land cover data 1km × 1km population data

Grid-based Analysis of Raster Data in ArcGIS

Resample land cover map into 10m × 10m for grid-based analysis

Grid-based Analysis of Raster Data in ArcGIS

Create grids(fishnet) in ArcGIS with the resolution of population data 1km × 1km

Grid-based Analysis of Raster Data in ArcGIS

 Extract each land use category by reclassify;  Use zonal statistics to get the number of cells in each grid;

Grid-based Analysis of Raster Data in ArcGIS

 Calculate the density of each land cover category in 1km × 1km grid;  Combine grid data with population data and check the relationship.

Grid-based Analysis of Vector Data in ArcGIS

Summarize vector data with grids for spatial visualization

Grid-based Analysis of Vector Data in ArcGIS

 Use standard Grids (Fishnet) Basic Grids Point data of bus stops +

Grid-based Analysis of Vector Data in ArcGIS

 Summarize vector data by spatial join

Grid-based Analysis of Vector Data in ArcGIS

 Visualize vector data

Conclusion

1. Grid is a useful unit to summarize both discrete data and continuous data, raster data can be regarded as data formed by grids; 2. Grid-based analysis for vector data is an efficient approach to connect vector data with raster data, raster can be resampled to fit the size of grid; 3. Grid-based analysis provides more detailed information than do municipal-scale statistics, and they are suitable for time series analysis, calculations, and comparison between mesh blocks.

References

 Bagan, H., & Yamagata, Y. 2012. Landsat analysis of urban growth: How Tokyo became the world's largest megacity during the last 40 years. Remote Sensing of Environment, 127, 210-222.

 Su, M. D., Kang, J. L., Chang, L. F., & Chen, A. S. 2005. A grid-based GIS approach to regional flood damage assessment. Journal of Marine Science and Technology, 13(3), 184-192.

 Richards, M., Ghanem, M., Osmond, M., Guo, Y., & Hassard, J. 2006. Grid-based analysis of air pollution data. Ecological modelling, 194(1), 274 286.

 Esri, 2015. GIS dictionary: Grid. Available online: http://support.esri.com/en/knowledgebase/GISDictionary/search (Accessed 10 June 2015)  Esri, 2015. GIS dictionary: Spatial Grid. Available online: http://support.esri.com/en/knowledgebase/GISDictionary/term/spatial%20grid (Accessed 10 June 2015)  Esri, 2015. ArcGIS Help 10.1. Discrete and continuous data. Available online: http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000007000000 (Accessed 11 June 2015)  Esri, 2015. ArcGIS Help 10.1. Esri Grid format. Available online: http://resources.arcgis.com/en/help/main/10.1/index.html#//009t0000000w000000 (Accessed 11 June 2015)