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?
Project file
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.
Name three common map elements
Title
Legend
North Arrow
Scale Bar
Neatline
Which data classification method would be most appropriate for displaying extremely high and extremely low values in a dataset?
Standard Deviation
What does GIS refer to?
(hint: not just the acronym)
GUS 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 (spheric) coordinates in angular units (degrees of lat, long)
Projected:
>use projection to transform spherical coordinates to planar
>use planar units (meter, feet) for recording coordinates
How are 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?
Unique values or single symbol maps
What is the difference between selecting features by attributes and selecting features by location?
Select by Attributes: a function used to choose a subset of features or table objects based on the values in one or more attribute fields.
Select by Location: a function used to choose a subset of features or table objects based on their spatial relationship to other features.
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.)
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 a feature class in comparison to a feature dataset?
Feature class is a set of geometric objects with similar attributes (points, polylines or polygons).
A Feature Dataset is a set of feature classes in a geodatabase that share a common coordinate system and can participate in networks and topology.
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)
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?
Topology defines the invariant rules of arrangement among geometric objects and the relationships between objects in a vector data file
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 data classification methods and when it would be appropriate for use?
equal interval
quantile (equal # of features)
standard deviation
natural breaks
defined interval
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