Geomatics Exam 1-9

Where is the origin of almost all spherical coordinate systems located?

The intersection of the equator and the prime meridian (a line of longitude that runs through greenwich, england)

Where is the origin of almost all GRID coordinate systems located?

There is no such location, the origin of a grid coordinate system may be any location on the earth. Most grid coordinate systems are created for specific areas like a continent or state.

What is a graticule?

A grid on a map or globe representing equally spaced (in angular units) lines of latitude and longitude

In terms of coordinate systems, what is DATUM?

A datum is an estimate of the earths ellipsoid shape. the datum must be estimated because the earths true geoid shape is too complex to calculate a perfectly accurate coordinate system.

Why is it important to consider the datum when developing a coordinate system?

Spherical coordinate systems identify locations based on angular measurements with the geometric center of the ellipsoid as the vertex of those angles. Given two different ellipsoids, the same angle may point to a different location on the surface of each ellipsoid. This also matters for grid coordinate systems because location of the origin of any grid coordinate system is defined using spherical coordinates.

is the following coordinate pair given in a spherical coordinate system or a grid coordinate system? 1,578,462 ft E, 658,555 ft N

Grid coordinate system. They always give locations in linear units.

Is the following coordinate pair given in a spherical coordinate system or a grid coordinate system? -83.889˚ E, 39.798˚ N

This is a spherical coordinate system. they always give locations in angular units (ie, degrees in this case)

What feature can be found at the coordinates 503,000 ft E, 608,000 ft N?

Buccleuch Park

What are the approximate coordinates of the intersection of Jersey Ave and French Street?

504,500 ft E, 604,000 ft N

You have a set of points showing the locations of sightings of a variety of threatened animal species in a wildlife preserve. What would be a good way to symbolize these points (using Bertin’s retinal variables) so that we identify each point by the species that was sighted there?

The best way would be to use a different shape or color for each species.

Given the data in the previous question, you want your map to show species grouped by class (mammal, reptile, etc.). What would be a good way to symbolize that data?

You could use a single color for each class, with each species in a given class having its own shape; or use a single shape for each class, with each species in a given class having its own color.

Different choropleth maps may show very different looking patterns even if they are based on the exact same data. How is that possible?

This is because the statistical values in a choropleth map need to be grouped into classes. Grouping those values into a different number of classes or grouping values into classes with different ranges (i.e. using different classification methods) can cause different maps of the same data to show somewhat different patterns.

I want to make a map showing the percentage of people in each municipality in New Jersey who take public transportation to work, should I make a choropleth map or a proportional symbols map? Explain your answer.

I should make a choropleth map. In this case, the number of people who take public transportation to work is normalized by the total number of people who work. Choropleth maps are the most appropriate choice for normalized data.

What does this map tell us?

All of the water from an area almost half the size of the continental U.S. flows into the Mississippi River, and down into the Gulf of Mexico.

What does this map tell us?

The most densely populated areas in Pennsylvania are small areas in the west (Allegheny County where Pittsburgh is) and the east (Philadelphia and its western suburbs).

Would this map best be described as a thematic map or a reference map?

This is a thematic map. It focuses on visualizing a single phenomenon, the distribution of populations in large cities across the continental U.S.

When discussing the scale of a map, what is the representative fraction?

The scale of the map as expressed a standard unitless ratio. E.g., for a map with a representative fraction of 1:1,000,000. Any distance measured between two points on the map is equal to 1/1,000,000 of distance between those two points in reality. Or, more usefully, for a given distance measured between two points on the map, the distance in reality is 1,000,000 times the distance measured on the map. So, if I’ve measured a distance of 1 inch between features on a map, the distance in reality is 1,000,000 inches.

If I am looking at a map that has a scale of 1:1000, and I measure a distance of 2.9 centimeters between two features on that map, what is the distance between those two features in reality?

2.9 * 1000 = 2,900 cm or (in more useful terms) 29 meters.

Given the map below, what is the approximate distance between the Busch Student Center and the Douglass Student Center?

~2.8 Miles (or just under 1½ scale bar lengths)

Mary lives about 1.75 miles from the Metuchen Rail Station. Using the map below, which was originally created at a scale of 1:24,000 but has subsequently been resized to fit this page, does Mary live at point A, B, or C?

It is impossible to know based on this map. Because the map was resized, the scale has changed. Since we don’t know what the new scale is, it is impossible to use it to make any meaningful measurements. (Also, you are most likely viewing these questions on a screen and not printed out, which means you are seeing this at a scale that is different from both the original map and the resized map if you were to print this page out.

Which of the maps below is at a smaller scale?

The map of France on the right is at a smaller scale. Remember, the easiest way to remember the difference between small and large scale when talking about maps is to think about how the individual features appear (as opposed to the geographic extent that the map covers). If features appear larger, then it is a larger-scale map. If they appear smaller, it is a smaller-scale map.

Why is it sometimes better to reduce the amount of detail when designing a small-scale map?

In small-scale maps, some features that would be informative at larger scales become unclear and create visual noise that distracts from the more important features on the map (e.g., features that show the phenomenon that a thematic map is intended to show or major structural features in a reference map).

Cartographic generalization describes a systematic approach to removing details to improve the legibility of a map. What are three general ways that we can do this?

We can simplify the shapes of features, use simpler geometry (lines rather than long narrow areas, etc.) or remove some less important features entirely.

What is meant by the term minimum mapping unit?

This is the size (total area or width) below which a feature should be omitted when performing cartographic generalization. It is also used when collecting data to decide whether a feature should be included in the dataset. In both cases, the MMU should be based on the scale at which the data will be used.

When the curved surface of the Earth is translated to the flat surface of a map, distortions occur in what four basic geometric characteristics of features?

Shape, area, direction and distance.

Is it possible to have a single map projection that preserves both the shapes and relative areas of features?

No. In order to correct for distortions to the relative sizes of features, we need to increase the distortion in their shape and vice versa.

What is a developable surface, in the context of map projections?

A developable surface is the flat surface onto which the curved surface of the Earth is projected. The developable surface is related to the surface of the Earth by bending it into one of three shapes: a cylinder, a cone, or an unbent plane. [Note: cylinders and cones can be flattened without distortion, reducing the overall distortion in some projections]

How do we minimize projection distortions across a relatively small area—say, New Jersey?

We can adjust the shape, size, and orientation of the developable surface such that the line (or point) of minimal distortion is centered on our study area.

Where is the greatest amount of distortion found on any given map projection?

Locations farthest away from where the developable surface would come into contact with the curved surface of the earth.

The map below shows known sites of soil and groundwater contamination, roads, and the land cover (e.g., water, forest, etc.) across the city of New Brunswick. Describe two things could you do to simplify this map and make it more legible?

a) Remove the pattern fill from the wetlands symbol and use a solid color instead. Pattern fills can be very useful in certain situations but, generally, solid fill colors on area features are clearer.

b) Remove the outlines from all of the land cover features. This might be a little hard to see when you are looking at the map as it is, but looking at simplified map below, you should be able to see how much clearer the urban land use areas of the city are without these outlines. Aside from removing visual noise, you avoid the potential for people to confuse those outlines for streets.

The map below shows projected retreat of coastal salt marsh in response to sea level rise in Union Beach, New Jersey. As sea level rises, some areas of marsh lost to persistent flood, while in other areas at slightly higher elevations, increased flooding promotes the conversion of other land cover types to salt marsh. However, an area will not convert to salt marsh if it is separated from existing salt marsh by impervious surfaces (roads, buildings, etc.). If you were to create a basemap for this map, what types of features would it make sense to include?

a) Water: We want to to relate the phenomenon to the source of flooding.

b) Elevation: The phenomenon is dictated by small changes in elevation.

c) Impervious surfaces: Marsh retreat is constrained by the presence of impervious surfaces.

d) Municipal boundaries are there, but labels would be helpful to indentify the area of interest and the surrounding towns.

In your own words, what is a GIS?

a) It is a computer-based system.

b) It works with spatial data and information.

c) It involves the collection, storage, analysis, output, and distribution of that data (not just making maps). It’s also important to understand that a GIS is not a software program, but a system in which software is one part.

What are the three components that make up a GIS?

Software, hardware, data

Name one GIS software program or platform other than ArcGIS

a) QGIS

b) Carto

c) Idrisi

d) MATLAB and R are not strictly GIS programs both provide mapping and spatial analysis functionality.

GIS Data has a unique data structure that is made up of two distinct parts. Name and describe these two parts.

a) Coordinate Data: the position on the Earth’s surface where each thing, event, or condition is located using a known coordinate system

b) Attribute Data: nonspatial information about each thing, event, or condition found in the coordinate data.

What is one way that GIS experts are needed in the GIS field?

a) To bring order to the massive amounts of data we are able to collect and store

b) To devise and perform complex spatial analyses

c) To design effective and communicative visualizations of those data and analysis results

d) To develop new software and hardware tools

What is one way that experts in other fields are needed in the GIS field?

a) To determine what spatial questions are important to ask

b) To bring knowledge of places, things, and events

c) To interpret GIS information within the context of other forms of information

d) To use GIS information to make management, planning, and design decisions

What is GIScience?

The field of research that provides the theoretical basis for geographic information systems.

What is one common criticism of GIS and a way that that criticism can be addressed?

a) “Access to GIS is limited to a privileged group.” This can be addressed by using participatory GIS approaches that give more control of the process to affected stakeholders.

b) “GIS is reductive and disconnected from its subject.” This can be addressed by making GIS analysis a part of a diverse approach to examining your phenomenon of interest.

c) “GIS data is inherently inaccurate.” All data has limitations. Not just GIS data. This can be addressed by considering each dataset’s intended use and how it is constructed and not trying to use a given dataset for a purpose for which it’s not suited.

In the lecture, we talked about four characteristics of data that are central to the conceptual model of GIS. That is, a dataset without these characteristics is not GIS data. What are these characteristics?

a) Spatial entities are represented by standard primitive structures. These are based on either feature geometry or grid cells.

b) Entities are grouped into distinct data themes. That is, a dataset should include fundamentally related entities like roads or soil types and not combine unrelated (or less closely related) entities together. For example, we would not include roads and soils in the same dataset. We usually wouldn’t even include roads and railroads in the same dataset. Each theme is stored as a separate dataset.

c) Data themes are treated as distinct layers. That is, GIS data is structured so that GIS software can display one set of features (or cells) on top of another like layers of trace paper, and we can change the way those layers are stacked one on top of the other.

d) Coordinate data is explicitly linked to attribute data. That is, the location information about features or cells that we view as a map (the coordinate data) is linked to the information we have about the characteristics or conditions of those features or cells (the attribute data), which we can view as a table. This allows us to easily get information about a feature or cell or to find the location of features or cells that have some characteristic or condition.

If I am doing a study on forested areas in a variety of municipalities, would it make sense to store the municipal boundaries and the forest boundaries in the same dataset? Why or why not?

No. Keeping the two data themes, municipal boundaries and forest boundaries, in separate datasets allows us to more easily ask other questions about each of those two themes individually or in relation to other themes. E.g., the locations of fire stations within each municipality within 10 miles of New Brunswick or the abundance of invasive Japanese honeysuckle across the region’s forests and woodlots.

Spatial data is usually stored using one of two basic data structures. What are these two structural models called? And what are two important differences between them?

a) Vector: Based on feature geometry concept; a single feature may delineate a complex linear or area entity; each feature may have many attributes associated with it; attribute table contains a record for each feature; generally bad for spatially continuous data

b) Raster: Based on grid cell concept; a linear or area element will be composed of multiple separate, independent cells; each cell may have only one attribute associated with it; attribute table contains only a list of values and the number of cells with each value; good for spatially continuous data

All of the students in one of my classes have added the same dataset to a map that they are working on for an assignment. Later, while working with that dataset for a project of my own, I accidentally delete a feature. What will happen the next time my students open their maps to work on their assignments?

The feature will be missing from their maps as well. Because the dataset is referenced rather than embedded, any change made to the data is reflected in any maps or projects that also reference that dataset.

What is the difference between embedding data and referencing data in a working document?

a) Embedding creates a copy of the content within the working file (e.g. adding an image to a word processing document).

b) Referencing does not create a copy of the content, but links to it from a separate file (e.g., linking an image on a webpage).

What is a data service? Name one advantage and one disadvantage of format.

a) Data services are datasets (or groups of datasets) that are stored on a remote server and accessed directly over the Internet rather than downloading a copy to your computer.

b) Advantages i) ii) Maps are updated automatically when the original data are updated (no need to check for updates and download newer version). ii. Requires less storage space on local system.

c) Disadvantages i) ii) Data may change or be removed when you don’t expect it to. May have limited functionality (editing, geoprocessing functions, or changing symbology may be restricted). iii) They can often be slow to render on your computer screen.

What is the difference between embedding data and referencing data in a working document?

a) Embedding creates a copy of the content within the working file (e.g. adding an image to a word processing document).

b) Referencing does not create a copy of the content, but links to it from a separate file (e.g., linking an image on a webpage).

The two raster datasets below have equally complex coordinate data. How is that possible?

Because raster data divides the area of interest into a grid, and each cell in the grid is distinct and independent. Breaking the area of interest into sub-areas of different land use types only requires us to change the attribute values of given cells. Unless we change the area of interest or the cell size, the grid itself is exactly the same. As a simplified example, shown below are two 5 x 5 cell grids. The size and number of cells is the same. The only difference is the coloration (and the associated attribute values) of different cells.

Given the two vector datasets shown below, unlike in the raster data in the example above, the dataset on the right is vastly more complex than the dataset on the left. Why is this?

he attribute values of existing subdivisions of the area of interest, we need to create new distinct features to represent each of those sub-areas. Because each individual feature in a vector dataset is fairly complex (particularly when it comes to polygon features), subdividing the area of interest rapidly increases the complexity of the data as a whole. Remember, each vertex (or point) in a vector dataset increases its complexity.

A spatial analysis in GIS is preformed through

geoprocessing operations

are used to answer questions related to the size and shape of features, and to the direction and distance between two features

Spatial measurements

of spatial data are used to answer questions related to the overall distribution of features

Descriptive summaries

is used to predict or infer what we might expect to find in a location given certain conditions

Modeling

methods are used to find locations that best fit a set of criteria or to most efficiently move through an area

Optimization

I want to predict the change in the distribution of salt tolerant plants in the Lower Raritan watershed if sea level were to rise by 4 feet over the next 50 years.

Modeling. I am trying to predict changes to distribution of specific plant types, given specified set of conditions.

I work for the school district. Several students at one of our local elementary schools havegraduated to middle school, while others are just starting first grade. My job is to update the bus route to pick up all of the students going to the elementary school in the least amount of time.

Optimization. I am trying to find the most efficient way for the bus to move through town, while making all of the required stops.

I have found a suitable location for my new city park, and I am considering different playground designs for it. To better understand who I’m building it for, I want to know—among other things—how many children between the ages of 5 and 12 live within a ten minute walk of the location.

Querying. I am trying to find how many kids live within a specified area surrounding a given location.

I run a pizza shop and I want to make sure that my pizzas are delivered in 29 minutes or less. This means that I can only reasonably deliver to locations within a 10-minute drive. In order to determine what addresses my business will deliver to, I draw a line around every part of the town that is within a 7-minute drive (you can’t be too careful).

Measurement. Here I am measuring a distance from a single point in all directions (along the road network).

How has the spatial distribution of trees in New York City changed since the Million Trees NYC initiative started in 2007?

Spatial. Here we are comparing the locations of all the trees in New York in 2007 to the locations of all the trees--including at least a million new ones--today.

How many trees are there in New York City now?

Not spatial. The locations of the trees (other than that they are within the study area) is not necessary to know how many there are.

primitive spatial structures

identify where something is

attributes

describes what is at that location

coordinates

measuring distance along two perpendicular axes

coordinate systems

indicate locations on the earth’s surface as its distance east and north of some broadly agreed upon origin point on the surface

grid coordinate systems

identify a location on a flat representation of a earth (the x and y axis grid basically)

spherical coordinate systems

identify a location on the surface of a spheroid rep of the earth (a globe) uses angular measurements (degrees)

north of the equator

latitude

east of prime meridian

longitude

datums are not

data

dips and bulges in the earths shape result in a complex shape called

a geoid

cells

individual units composing to a grid. makes up the grid basically. not the exact same as other cells-they are independent of their own

landscape mosaic

conceives of the composition of an area as a mosaic of more or less discrete patches where certain conditions are met (specific vegetation communities, species habitat, etc.).

In geomatics, the most important are

feature geometry (dividing space into discrete, point, lines, and areas) and grids (dividing space into a set of ordered units (cells) each with the same size and shape

scale

indicates the size relationship between a representation and the thing it represents

map scale

defines precisley how much smaller features represented in a map are than those features in reality

representative fraction

a simple ratio between the map distance and the ground distance

verbal scale

converts the numerator and denominator of the RF to different units for easier interpretation (1 in (map) = 2000 ft (ground)

scale bar

represents the relationship between map distance and ground distance graphically

small scale map covers a

LARGE geographic area

a large scale map covers a

SMALL geographic area

the terms are based on the number given by the

representative fraction

the smaller the scale (like when its zoomed out) the…

less detail it should include

why would you not include the maximum amount of detail at all scales?

visual noise/it can be hard to read if zoomed in with too many visual distractions

map projections are

algorithms that mathematically account for distortions that occur in the process of projecting a 3D curved surface to a 2D flat surface

the flat surface onto which the curved earth is projected is called the

developable surface

What is GIS?

a) It is a computer-based system.

b) It works with spatial data and information.

c) It involves the collection, storage, analysis, output, and distribution of that data (not just making maps).

It’s also important to understand that a GIS is not a software program, but a system in which software is one part.

vector data is

based on feature geometry, has complex coordinate data, and can have many associated attributes

Raster data is

•based on grids, has simple coordinate data, and can have only one associated attribute.

The most common file-based file format for vector data is the

shapefile

Geodatabases

•store vector, raster, and tabular data together in a single relational database. ​

data services are

accessed directly from the remote server and streamed to the user’s GIS software

GIS software…

references data, reading from the original data files rather than embedding a copy of the data in the map project

GIS software locates referenced datasets using small bits of code called

file paths

map scale defines…

precisely how much smaller features represented in a map are than those features are in reality

scale represents…

the size relationship between a representation and the thing it represents

cartographic generalization

is a systematic approach to limiting detail at smaller scales to improve map clarity.

It is possible to localize projections by systematically…

moving the line of least distortion closer to the map’s area of interest.

Converting a curved 3D surface onto a flat 2D surface…

introduces distortions features and to spatial relationships among features.