GIS Basics
What is the name given to the entire dataset where spatial data are accessed from their original location for a given map or series of maps in ESRI tools?
ESRI Project file
(would also accept Geodatabase)
What is a projected coordinate system? Give an example of one.
A mathematical transformation that converts spherical units of latitude and longitude to a planar x-y coordinate system.
Examples: conical, utm, state plane, etc.
What are the two main types of raster data?
What types of data are presented in each?
Discrete Raster: categorical/nominal data
ex: land use codes, soil types
Continuous Raster: variable quantities over area
ex: elevation, weather, etc.
Note: ALL rasters are thematic!Name three common map elements found in a final map layout.
Title
Legend
North Arrow
Scale Bar
Neatline
Which field type would be appropriate for an attribute in a vector dataset documenting rainfall to the nearest thousandth of a centimeter?
Floating Point/Float
What does GIS refer to?
(hint: not just the acronym)
GIS is a system of hardware and software designed to capture, store, query, analyze and display geographically referenced data
What is the difference between projected and unprojected coordinate systems?
Unprojected:
- based on 3d earth representation
- no projection used
- uses geographic (spherical) coordinates in angular units (degrees of lat, long)
Projected:
- 2d depiction, transforms spherical coordinates to planar
- use planar units (meter, feet) for recording coordinates
How are map characteristics stored in vector data?
Vector data models can store large quantities of attribute data in tables
What type(s) of map is(are) best suitable for nominal data?
Give an example of a nominal dataset and how it might be mapped.
Unique values or single symbol maps
Cities/capitols - single symbol stars, etc. (names/symbols or colors only)
Which tool is used in ArcGIS Pro to change labels, display colors or icons of a given vector dataset?
Symbology
Name vector data geometry.
Give an example of each.
Line, Point, Polygon
What do projected coordinate systems account for, and why do we use them?
Projected coordinate systems optimize map data for specific study areas (state, city, continent, etc.)
X and Y coordinates correspond to locations on the Earth's surface, optimized for 2d viewing of a given land mass.
We use different projections because the world is not flat!
Name three advantages or disadvantages of vector data model compared to raster
Advantages Raster:
Good for complex analysis (e.g. map algebra)
Efficient for overlays
Data structure common for imagery
Advantages Vector:
Compact data structure
Efficient for encoding topology
True representation of shape
Disadvantages Raster:
Large datasets
No topology
Maps less "realistic“
(“blocky”)
Disadvantages Vector:
Complex structure
Overlay operations difficult
May require more preprocessing (e.g. cleaning topology)
What is scale?
What does a scale of 1:10,000 mean?
Is 1:10,000 a smaller or larger scale than 1:1000?
Scale: ratio of distance on the map to distance on the ground
- Every 1 inch or cm on the map represents 10,000 inches or cm on the surface of the earth.
- 1:10,000 a smaller scale than 1:1000
What kind of map displays numeric values as a single color intensity between light and dark polygons?
Choropleth map: the color represents a value (or range of values) in a numeric data field/attribute
What is RGB relative to GIS and map data?
RGB: A method of specifying color using a mixture of red, green and blue hues/saturation/values (HSV) on a scale of 0-255 for each.
Explain the difference between a GIS layer and a shapefile.
Layer file: stores spatial data and display properties
Shapefile: a spatial data model used by GIS software (minus display properties), typically relied upon in legacy software.
Shapeflies are more of a stand-alone product, whereas layers are associated with specific ESRI projects in ArcGIS Pro.
Compare and Contrast:
feature, feature class, feature dataset
Feature: a spatial object with one or more x-y coordinates and one or more attributes in a single record. (one point, line or polygon)
Feature Class: a set of similar objects with the same attributes stored together in a single file. (a collection of points, lines or polygons)
Feature Dataset: a container for feature classes that share the same coordinate system and area extent. (a collection of vector files with shared topology.)
Which map type works best for the following data?
state names
county population
number of murders by city
---
1. graduated symbol
2. graduated color (choropleth)
3. unique value
state names 3
county population 2
number of murders by city 1
---
1. graduated symbol
2. graduated color (choropleth)
3. unique value
Describe GIS “view” of the world
Combines different layers of information stored as either raster or vector datasets that together create a view of the real world.
What is Topology?
Give one example of a topological data error.
Topology defines the invariant rules of arrangement among geometric objects and the relationships between objects in a vector data file
Example Errors: Dangle, overshoot, undershoot, gap, pseudonode, loop, improper intersection
What is map Positional Accuracy?
Positional Accuracy: a measure of the likelihood that features on a map are actually in the locations specified on the surface of the earth.
What is MAUP?
Modifiable
Area
Unit
Problem
MAUP consists of statistical and visual issues caused by aggregating measured data using arbitrary areal units such as political boundaries. this can be overcome by normalizing data by area, population etc.
Explain two map data classification methods and when it would be appropriate for use?
Equal Interval - When an equal quantities of items exist in each category to be mapped.
Quantile - When data are normally distributed and critical values are necessary at .25/.75 percentiles.
Standard Deviation - When outliers/extreme high or low values within a dataset are important to display.
Natural Breaks - When data have "natural breaks" along a typical statistical distribution (assuming normal, but not always) This is often the default selection for classification.
Defined Interval - User defined interval to highlight categorical or special breaks within the data.
What are two cardinal rules for spatial data file storage & naming conventions?
- <13 characters
- no spaces
- avoid numbers
- avoid special characters
- often use “shorthanded” names