Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
10 Cards in this Set
- Front
- Back
|
How are GIS software different from most other software?
|
GIS software allow us to look at spatial data, something other softwares do not. It helps analyze relationships and trends among said spatial data. In some cases it is the only way spatial-related problems can be solved. GIS is particularly helpful in addressing environmental issues by locating the source, location and extent of adverse environmental impacts.
|
|
|
How is an entity different from a cartographic object?
|
An entity is a real-world item or phenomenon that is represented in a GIS system or database whereas a cartographic object the digital representation in GIS of said real-world entity.
|
|
|
Describe the successive levels of abstraction when representing real-world spatial phenomena on a computer. Why are there multiple levels, instead of just one level in a spatial data representative?
|
Moving down the successive levels of abstraction, you first pass through the data model, which is a set of polygons or closed areas that record the edges of distinct land uses. The next level is the data structure, which has coordinates for all of the polygons and then the machine code stores everything in binary. While it gets less recognizable as it travels through levels, it is computer-compatible.
|
|
|
Define a data model and describe three primary differences between the two most commonly used data models.
|
A data model is a method of representing spatial and aspatial components of real-world entities on a computer. The two primary models are vector and raster models. A vector model is most like a typical map that we think of. It has points, line and polygons. Size and dimensions of the entity are not important in these models, only the location. A raster model divides the area into a grid-like pattern and every square has a value. This makes it much bigger than a vector model in terms of file size. It is the natural way to represent continuous data. Raster models are relatively simple, compared to vector models and are east to modify or program. Vector models can have continuous curves but are poor for images, whereas raster models are good for digital images but have stair-step curves.
|
|
|
What is topology and why is it important? What is planar topology and when might non-planar be more useful than planar topology?
|
Topology is shape-invariant spatial properties of line or area features such as adjacency, contiguity, and connectedness, often recorded in a set of tables. It is important because it greatly improves the speed, accuracy and utility of many spatial data operations. Planar topology assumes that all features occur on a two-dimensional surface. There cannot be any overlaps. Non-planar topology allows for overlaps and assumes it is mapping a three-dimensional world. This might be useful for mapping bridges.
|
|
|
What are the respective advantages and disadvantages of vector data models versus raster data models?
|
Raster models has continuous data, are relatively simple to modify, need much more storage space, may be slow, their floor is set by cell size, good for images but may have stairstep edges.
Vector models are ususally complex and hard to modify. They can be compressed much more, they are preferred for network analysis, are only limited by positional measurements and are map-like with continuous curves. |
|
|
Under what conditions are mixed cells a problem in raster data models? In what ways may the problem of mixed cells be addressed?
|
Normally each cell receives one value, so when there are multiple values for one cell, difficulties arise. One solution is to simply represent only one feature. This means there may be data loss. Another solution is to make the cells small enough so that there will ever be multiple features in one cell. This means the data set may have to get a lot larger. There are ways to record multiple instances in one cell, but it may slow access.
|
|
|
What is an ellipsoid? How does it differ from a sphere? What is the equation for the flattening factor?
|
An ellipsoid is a three-dimensional figure whose plane sections are ellipses or circles. The equatorial radius is always greater than the polar radius. A sphere is a perfect circle in which both radii are equal. The flattening factor is: (a-b)/a
|
|
|
Why do different ellipsoids have different radii? Provide three reasons.
|
Originally, geodetic surveys were separated by large bodies of water so this affected measurements. Ellipsoids were also fit for each country, region or area being surveyed and there isn’t one best ellipsoid for every region on earth. This meant there were different radii. New technology has created new best ellipsoid that averages differences all over the earth, but different ellipsoids are better for different areas of the earth.
|
|
|
Can you define a parallel or horizontal meridian in a geographic coordinate system? Where do the horizontal and vertical zero lines occur?
|
A meridian is simply a line of constant latitude or longitude, typically longitude. That being said, it runs east to west or north to south and in a Mercator or Transverse Mercator, it is the line of intersection and the line of least distortion. In a vertical meridian, it typically starts and stops in Greenwich. The horizontal meridian hits the Earth at the equator.
|
