Week 4 Notes - Spatial Data & GIS Operations in R

Published

September 29, 2025

Key Concepts Learned

  • Why Spatial Analysis Matters
    • Real Policy Questions Need Spatial Answers
    • Algorithmic Bias
  • Spatial Data Fundamentals
    • Vector Data Model矢量数据
      • Points, Lines, Polygons with Geometry(Shape and location)&Attributes(Data about that feature (population, income, etc.)
    • sf Package:Simple Features for R
      • Key principle: Spatial data is just data.frame + geometry column
    • Raster Pattern
      • Shapefile(shp,shx,dbf)
      • geojson(不需要三个，全部涵盖)
      • KML/KMZ (Google Earth)
  • Spatial Operations
    • Spatial Subsetting空间子集
    • Understanding the .predicate Parameter
      • Basic structure: st_filter(data_to_filter, reference_geometry, .predicate = relationship)
    • Spatial Relationships
      • st_touches(Share boundary, no interior overlap)
      • st_intersects(Any overlap at all)
      • st_within(Completely inside)
      • st_contains(Completely contains)和intersects主宾位置互换
      • st_overlaps()
      • st_disjoint(No spatial relationship)
  • Geometry Operations
    • Buffer Operations
    • Intersection Operations(Find overlapping areas)
      • st_intersection(Calculate / Clip)这是一个几何运算。它计算出 x 和 y 几何形状实际重叠的部分。返回一个新的 sf 对象。它的几何形状是 x 和 y 相交后产生的新形状。通常会合并 x 和 y 的属性数据。
      • st_filte(Select)这是一个逻辑判断。它检查 x 中的每个要素是否与 y 存在空间关系，然后返回 TRUE 或 FALSE，并以此来筛选 x。返回 X 的一个子集。保留下来的行是原始的、几何形状未改变的行。只保留 x 的属性数据。
    • Union Operations
    • Spatial Aggregation 空间聚合
  • Coordinate Reference Systems
    • Geographic vs. Projected Coordinates
      • GCS(Latitude/longitude coordinates, Good for: Global datasets, web mapping,Bad for: Area/distance calculations)
      • PCS(X/Y coordinates on a flat plane, Good for: Local analysis, accurate measurements, Bad for: Large areas, global datasets)
    • Common Coordinate Reference Systems坐标参考系
      • WGS84 (EPSG:4326)Geographic system
      • Web Mercator (EPSG:3857)Projected system
      • State Plane / UTM zones (Different zones for different regions)
      • Albers Equal Area(Good for demographic/statistical analysis)
  • Elipsoid
    • Step1:Approximate Earth Shape with Elipsoid
    • Step2:Tie Elipsoid to the real earth(Datum)
    • Step3:Put dowm Lat/Long grid
  • Example(Geographic(Geodetic) coordinate systems-3D model, lat/long)
    • 1866 Clark,origin point,Meades Ranch,Kansas(North American Datum 1927 NAD1927)最开始就用这个
    • NAD83,GRS80,earth centered
    • WGS84,earth centered
  • Project 3D Coordinates(由中间向两侧变大distorted！)
    • Line of Tangency
    • Cylindrical-Mercator
    • Transverse Cylindrical
    • Conic(同纬度)
    • Planar（arctic）
  • Projected Coordinate System-nondistorted
    • UTM 6 zones 6 degrees
  • Checking and Setting CRS
    • pa_counties_projected <- pa_counties %>% st_transform(crs = 3365)

## Coding Techniques

## Questions & Challenges

Connections to Policy

  • [How this week’s content applies to real policy work]

Reflection

  • [What was most interesting]
  • [How I’ll apply this knowledge]