GIS Generally Flashcards
Spatial Data
data with a geographic location, representation, or reference point that it describes.
Cartography
the science of map making, including data inclusion, layout, elements, colors, and design. As much as it’s a science, it’s an art form.
Shapefile
An Esri proprietary data format for storing geographic data. Very cross-GIS compatible, but limiting in many aspects. Often misused to mean any geographic dataset as in “could you send me that shapefile?”
Layer
multiple meanings in a GIS context:
a. The distinct data elements that compose a map document, ordered one on top of the next for GIS drawing order (top is drawn last and seen first)
b. A single data element, saved into a GIS file format along with its associated symbology.
Scale
the ratio of the size of elements on screen or in print on the map to their size in the real world
Raster
spatial data that stores location based upon a single origin point and a data stream of known width, height, and resolution. Often used for continuous surfaces.
DEM-Digital Elevation Model
A specific use case of raster data where the pixel value represents the elevation of areas covered by the pixel. Sometime called a DTM (digital terrain model) or DED (digital elevation dataset).
Vector
spatial data that stores location using Cartesian coordinate locations.
a. Point – A single spot in (usually) two dimensional space. Attributes represent only that location (and sometimes are inferred to represent nearby locations).
b. Line (Polyline) – Multiple points connected to represent all locations in between along the connection.
c. Polygon – Multiple polylines connected to create a boundary. Polygon zones are generalized representations where all locations contained within the boundaries are considered to have the same property.
Coordinate System/Spatial Reference
defines the origin point, coordinate space, and geoid for a dataset’s spatial data.
a. Datum – the origin point of the coordinate system and information required to accurately define an origin, like a surface model.
b. Geographic Coordinate System (GCS) – A coordinate system that specifies latitude and longitude as coordinates.
c. Projected Coordinate System – similar to and includes a GCS. “Projects”/transforms coordinates into a new coordinates system to display a map in 2D space. Sometimes referred to as “the projection” of a dataset.
Resolution
the density of data of a raster dataset or rasterized map document. Sometimes used to mean the density of data in any dataset. For raster datasets, this value is expressed as the length of the side of a pixel (e.g.: 10m pixels). For rasterized graphic formats, it is most commonly expressed in pixels per inch of paper (ppi) or dots per inch of paper (dpi) and a good target to reach is 300 dpi for clear prin
Geoprocessing
the practice of using GIS tools to process, transform, filter, and query GIS data.
Python
- Basemap – a prerendered set of mapping data that can be placed below the data of interest to quickly create a map with context. Frequently, a basemap is served up over the Internet by a basemap server and loaded on the fly by your GIS.
a programming language with capabilities for GIS analysis. Useful for automating tasks in GIS.
Join
The use of a common attribute to link data tables in order to access the attributes of one along with the other or assign the attributes of one to the other based upon a key value. When this is the record ID of the other dataset, it’s often a foreign key. For example, summary statistics tables built for HUC12s can be linked back to the HUC12 by the HUC12 ID.
Spatial Join
Similar to a Join in that it transfers attributes, but the linkage used to connect the datasets is the location of each item. I find this to be the “hammer” of GIS.
Symbology
The representation of a particular dataset in a map document.
