Research Guides: ENVS 250: Geographic Information Systems: GIS Data Formats

GIS Data Formats

VECTORS
Vectors are geographic features of the same type that are stored in a file as strings of coordinates that form points, lines, or polygons (areas) in conjunction with attributes that describe the features. Vectors are drawn to a specific scale with a particular coordinate system and map projection that allows them to be depicted visually and overlaid with other geospatial data. Common formats include shapefiles, geopackages, and GeoJSON.

1. Points - Specific locations like parks, museums, schools, hospitals, etc.
Minto Brown Park (44.924852N and -123.073225W)

2. Lines - Linear features like roads & rivers.
Interstate 5 (I-5) [(44.9429, -123.0351), (44.9430, -123.0355), (44.9435, -123.0360)]

3. Polygons - areas like parks boundaries or lakes or burn areas or safety zones.
Park Boundary: [(44.9429, -123.0351), (44.9430, -123.0355), (44.9435, -123.0360), (44.9429, -123.0351)]

RASTERS
Rasters are a continuous surface of grid cells of equal size, where values of a cell denote a feature type or attribute and the size of the cells indicates resolution. Think of a grid with dots like pixels, and each dot represent a specific value. They are structured like other digital images except they are georeferenced: rasters have been created or warped to a particular coordinate system and map projection so they can be overlaid with other geospatial data. Formats vary widely.

By analyzing this grid, you can derive valuable insights about the region's land cover. In this grid:

1 represents forest
2 represent urban areas
3 represent water bodies
4 represent agriculture

TABLES (SPREADSHEETS)
Tables are spreadsheet records that represent a geographic feature with attributes (columns) that describe that feature, but the records lack geometry and cannot be displayed visually. To visualize tables, the records can either be joined to a corresponding vector file of the same features using a shared unique identifier, or can be plotted as a point-based vector if the records include attributes for XY coordinates. Common formats include delimited text (CSV, TSV) and spreadsheet files.

This GIS dataset contains inform about different locations in a city, including their coordinates, names, and types of points of interest (POI). Multiple characteristics about one location are represented in each row.

ID is a unique identifier for each location.
Name represents the name of the location.
Latitude and Longitude are the geographic coordinates of the location.
Type indicates the type of point of interest (e.g., park, landmark, square, bridge, monument).

By storing spatial data in this tabular format, you can easily manage, query, and analyze the information using GIS software. You can create maps, perform spatial analysis, and visualize the distribution of different types of points of interest across the city.

SPATIAL DATABASES
Spatial databases are containers that hold a collection of vector, raster, and tabular data. Depending on the GIS software you use, you access the databases by establishing a connection to them or navigating them the way you would a file folder. Common file-based formats include: file geodatabases (gdb, default ArcGIS format), personal geodatabases (mdb older ArcGIS format), and Spatialite (open source).

IMPORTANCE OF METADATA & DATA STRUCTURE
Maintaining and staying on top of your metadata is essential. It helps to manage, query, match, and analyze data. Take it from experience, document your metadata; it will pay off big time!!!

ENVS 250: Geographic Information Systems

Willamette University Libraries