What are Data formats?
There are two data formats that GIS is handy with: Vector and Raster data formats. Both data systems store spatial and attribute data, but in different ways. Both are georeferenced, meaning that the information is tied to a specific location on the earth’s surface using x-y coordinates defined in a standard way: a coordinate system.
Vector model: stores discrete data—eg, points (no dimension), lines (1D), and polygons (2D).
- Benefits of vector models:
- Can store individual feature classes, such as roads and parcels, with high degree of precision
- Linked attribute table provides great flexibility in the number and type of attributes that can be stored about each feature.
- Ideally suited for mapmaking because of high precision and detail—it is a compact way of storing data
- Ideally situated to certain types of analysis problems, such as determining perimeters and areas, detecting whether features overlap, and modeling flow through networks.
- Poorly adapted to storing continuous surfaces, such as elevation or precipitation.
- Contours lines can be used to represent surfaces, but calculating derived information from contours such as slope, flow direction, and aspects, is difficult.
- Some analysis is more time consuming
Raster Model: stores continuous data—set of spatial data represented as series of small squares called cells or pixels. Each pixel contains a numeric code indicating a single attribute, and the raster is stored as an array of numbers. Eg, DEM.
- Benefits of Rater model:
- Ideally suited to store continuous information because each cell can have a value completely different from its neighbors.
- Simple and rapid analyses.
- Extensive set of analyses tools for raster available.
- Drawbacks of raster:
- Suffer from trade-offs between precision and storage space to a greater extent than vectors do.
- Can store only one numeric attribute per raster, whereas vector can store hundreds of attribute values for each spatial feature and can handle text data more efficiently.