Question 1

Briefly explain differential correction of GPS data.

Accepted Answer

Differential correction of GPS data is a technique used to improve the accuracy of Global Positioning System (GPS) position estimates. The fundamental principle behind differential correction is the use of a reference station at a known location to measure errors in the GPS signal.

Here's how it works:

1. A reference station, which is a GPS receiver at a precisely known fixed location, continuously receives signals from GPS satellites and calculates its position based on those signals.

2. Because the exact location of the reference station is known, any difference between the calculated position and the known position is considered to be due to GPS signal errors. These errors can be caused by various factors, including atmospheric conditions, satellite clock inaccuracies, and multipath effects.

3. The reference station then computes corrections for these errors and either stores them for post-processing or broadcasts them in real-time to nearby GPS receivers that are known as rovers.

4. The rover GPS receivers, which are the units in the field that are trying to determine their own positions, apply these corrections to their own satellite data. This process can be done in real-time (known as Real-Time Differential GPS or RTK GPS) or after the fact (post-processing).

5. By applying these corrections, the accuracy of the rover's position estimate is significantly improved, often achieving sub-meter or even centimeter-level precision, depending on the system and conditions.

Differential correction is widely used in applications where high accuracy is essential, such as surveying, precision agriculture, construction, and scientific research. It is an important tool for overcoming the inherent limitations of standard GPS and providing users with the precise location information they require for their specific tasks.

Question 2

What is a geoportal?

Accepted Answer

A geoportal is an online platform that provides access to a wealth of geographic information and services. It acts as a centralized gateway where users can find, share, and use geospatial data, maps, and tools. Geoportals are designed to facilitate the discovery and utilization of geographic information by a wide range of users, from government agencies and private enterprises to researchers, non-profit organizations, and the general public.

The core functionalities of a geoportal include:

1. **Data Discovery:** Users can search for geospatial data using keywords, geographic bounding boxes, or other metadata criteria. This makes it easier to find specific datasets among potentially thousands of available records.

2. **Data Access:** Geoportals provide direct access to geospatial data, which can often be viewed through an integrated map viewer. Users may also be able to download data in various formats for use in their own geographic information system (GIS) software.

3. **Data Management:** They offer tools for uploading and managing geospatial datasets, including the ability to update, delete, or modify information. This ensures that the data remains current and relevant.

4. **Metadata Cataloging:** Geoportals use metadata (data about data) to describe the content, quality, condition, and other characteristics of the geospatial data. This helps users understand the context and limitations of the data they are accessing.

5. **Map Creation and Sharing:** Users can often create their own maps by combining different layers of data. These maps can then be shared with others or embedded in websites.

6. **Services Integration:** Many geoportals integrate with other web services, such as Web Map Services (WMS) and Web Feature Services (WFS), allowing for dynamic interaction with geospatial data hosted elsewhere.

7. **Community Engagement:** Some geoportals include forums, user groups, and other collaborative features that enable users to connect with each other, share expertise, and work together on geospatial projects.

Geoportals are important tools for supporting decision-making processes that require spatial analysis, such as urban planning, environmental management, disaster response, and transportation planning. They help to promote the use of geospatial data and make it more accessible to those who need it, ultimately contributing to more informed and effective policy and planning. Examples of geoportals include the United States' data.gov, the European Union's INSPIRE Geoportal, and the Global Earth Observation System of Systems (GEOSS) Portal.

Question 3

COGO (Coordinate geometry) can convert ______ into spatial features:
A) survey data
B) street addresses
C) GPS data
D) remotely sensed data

Accepted Answer

COGO (Coordinate Geometry) is primarily used to convert survey data, which includes precise measurements of angles and distances, into spatial features.

Question 4

What are the spatial resolutions of DEMs available from the USGS?

Accepted Answer

The answer of What are the spatial resolutions of DEMs...

Question 5

A GPS receiver can collect the height in addition to the horizontal position of a point on the Earth's surface.

Accepted Answer

A GPS receiver can determine a three-dimensional position (latitude, longitude, and altitude) by receiving signals from multiple GPS satellites, thus providing both horizontal positioning and height information.

Question 6

Which of the following is considered an automatic digitizing method?
A) digitizing using a table digitizer
B) digitizing using a scanner
C) on-screen digitizing

Accepted Answer

Digitizing using a scanner is considered an automatic digitizing method because it automatically converts images or maps into digital form without manual tracing or plotting.

Question 7

Which of the following organizations has been coordinating the development of the National Spatial Data Infrastructure (NSDI) in the United States?
A) Federal Geographic Data Committee
B) Natural Resources Conservation Service
C) US Forest Service
D) Environmental Protection Agency

Accepted Answer

The Federal Geographic Data Committee (FGDC) has been coordinating the development of the National Spatial Data Infrastructure (NSDI) in the United States, aiming to ensure that spatial data from multiple sources (federal, state, local, and tribal governments) is available and easily integrated to enhance understanding of our physical and cultural environment.

Question 8

A clearinghouse is __________, and a geoportal is _________:
A) data-centric, service-centric
B) service-centric, data-centric

Accepted Answer

A clearinghouse is a data-centric system that provides access to a variety of data sources, while a geoportal is a service-centric system that provides access to a variety of geospatial services.

Question 9

Suppose you are asked to convert a paper map to a digital data set. What methods can you use for the task? Briefly describe how each method works.

Accepted Answer

The answer of Suppose you are asked to convert a...

Question 10

GPS readings of longitude and latitude are based on:
A) WGS84
B) NAD29
C) NAD83
D) none of these is correct

Accepted Answer

GPS readings of longitude and latitude are based on the World Geodetic System 1984 (WGS84), which is the standard coordinate system used by the Global Positioning System.

Question 11

The source map can greatly influence the quality of a digitized map. Provide an example that supports the statement.

Accepted Answer

The answer of The source map can greatly influence the...

Question 12

The spatial resolutions of Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) are approximately:
A) 1000, 500, and 250 meters
B) 10, 5, and 1 kilometer
C) 250, 100, and 10 meters
D) 3, 2, and 1 kilometer

Accepted Answer

The Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) offers three primary global spatial resolutions: approximately 1000 meters (30 arc-seconds), 500 meters (15 arc-seconds), and 250 meters (7.5 arc-seconds).

Question 13

Nowadays we can download free LiDAR data.

Accepted Answer

LiDAR data is increasingly available for free through various platforms and government initiatives, allowing users to download it for research, environmental monitoring, urban planning, and other applications.

Question 14

What is SSURGO?

Accepted Answer

The answer of What is SSURGO?...

Question 15

On-screen digitizing has gained its popularity among GIS users. Name two advantages of on-screen digitizing compared to tablet digitizing.

Accepted Answer

The answer of On-screen digitizing has gained its popularity among...

Question 16

The scanning method for digitizing involves both rasterization and vectorization. Explain what each process accomplishes.

Accepted Answer

The answer of The scanning method for digitizing involves both...

Question 17

The U.S. Census Bureau offers KML files of nation-based and state-based boundaries for download. What is the main application of these files?

Accepted Answer

The answer of The U.S. Census Bureau offers KML files...

Question 18

Digital orthophotos do not contain image displacement or distortion.

Accepted Answer

Digital orthophotos are corrected for lens distortion, camera tilt, and terrain relief, resulting in a uniform scale and accurate representation of the Earth's surface without image displacement or distortion.

Question 19

A text file with the fields ofx-,y-coordinates can be converted to a digital map.

Accepted Answer

A text file containing x-, y-coordinates can be processed by mapping software to create a digital map, where each pair of coordinates represents a point on the map.

Question 20

List three different methods for creating new GIS data.

Accepted Answer

The answer of List three different methods for creating new...

Quiz 5: GIS Data Acquisition