File Name: vector and raster data models in gis .zip
In the previous topics we have taken a closer look at vector data.
- GIS Introduction by David J. Buckey
- Geospatial Data Models
Data expands the richness of a map: giving the user a deeper, more insightful view of an area or project. Remember, as a concept, GIS can be defined as the intersection of data and location. In the last chapter, we covered the location component: mapping. However, GIS mapping requires more than coordinates. Vector data is, essentially, a list of coordinates: one that provides instructions on how an image should be rendered. Vector images are high-fidelity graphical representations of an image or shape.
This graphical property means that vector images are infinitely scalable. They can be enlarged or reduced with no quality loss. Vector images can only be created and manipulated with a computer program like Adobe Illustrator or Sketch.
You cannot, for example, use a camera to capture a vector image. Vector points are basically x,y coordinates. In GIS mapping , vector points illustrate features too small to be drawn at scale. For example, if you're creating a map of a specific city, you'd use lines to draw the city's boundaries. However, create a map of the entire country and that boundary is no longer visible - so a labeled point is used instead.
This image of Colorado illustrates this concept perfectly: the state capital being representated as a labeled point. They have distinct start and end points and, though they can intersect with one another, a single line will not intersect with itself. Vector lines are used to represent linear features such as rivers, roads, and trails. Color, thickness, and line type solid or dashed are used to denote unique features, or unique attributes of the same feature.
For example, a heavily trafficked highway might be drawn with a thick line, whereas the residential roadway would be much thinner. Moreover, streets could be solid black lines, while the river might be dotted and blue.
Stylistic choices like these are at the map makers discretion, but can add depth and visual interest to the map. Topographic map represented with polygons [Source]. Polygons represent features with distinct boundaries: states, property lines, lakes, etc. Where vector data coordinates that create an image is somewhat abstract, raster data is quite literal.
In GIS mapping , raster data generally represents surfaces. Unlike vector data, raster data cannot be scaled infinitely. Enlarge it too much and it becomes fuzzy and pixelated. Stretch too much in one direction and the features distort. Raster image of trees [Source]. Vector drawing of trees [Source]. Despite these limitations, raster data does have advantages; chiefly, it provides a level of detail not possible with vectors. Photographs provide an immense level of contextual detail and represent the subleties of light and color quite accurately.
Consider the images shown here. The first depicts vector images of trees, the other is a raster photograph. Both images depict trees accurately. However, the raster photograph is not only more detailed, but is more visually nuanced.
In terms of GIS mapping , raster data comes in two types: discrete and continuous. Discrete data can only take specific values, whereas continuous data can take any value within a range. For example:. The number of people in a room is a discrete value. Continuous data is more flexible, including values such as height, weight, and length. A person's height can be any value within the range of human heights. Continuous and discrete data are complementary, but do have different applications.
Each grid cell contains some level of gradation. Continuous rasters are often used to represent data that experiences gradual change: temperature, population, elevation, etc. Map of discrete data [Source]. Map of continuous data [Source]. What's the difference between discrete data and continuous data?
Non-topological data is the location. It consists of x,y coordinates and does not include a third dimension the z coordinate. Consider an elevation map. The non-topological data x,y coordinates illustrate the base terrain, while the associated attributes z coordinates represent the elevation profile.
Drought conditions in the United States are a good example of a map that could be stored and shared as a shapefile. The map of the United States would be the non-topological data, while the drought conditions data would be the attributes. Street map Non-topological data [Source].
Elevation map Topological data [Source]. Though shapefile sounds singular, there is actually a minimum of three file types that must be present in order to render a shapefile correctly. There are over 60 GIS file types , each with unique characteristics and use cases. The sheer number of geospatial file formats can be overwhelming. As such, they're not optimal for use on websites.
That said, they do offer the most flexibility in terms of editing and adding transparency, tags, and layers. The metadata acts as instructions on how to locate the file on the map. File geodatabases allow users to store all thematically related data in a single database.
Each database can organize and store vector and raster files, relationship classes, attribute tables, and spatial data. Geodatabases and Shapefiles can achieve similar goals. However, geodatabases offer significant advantages:.
Personal geodatabases were the precursor to file databases and are the default for Microsoft Access. To learn more about personal databases, as well as the differences between the two database types check out the article below.
Learning resource: What is a Geodatabase? Personal vs File Geodatabase. They also contain a variety of configuration options that, though they add significant value to Google Earth as an application, limit the use of KML files elsewhere.
As text files, they are easily the simplest file format here, making them ideal for transferring data between programs. For this to be successful, the CSV file must have columns for both x and y coordinates. Originating as the combination of the words 'radar' and 'light,' the term LiDAR is now used as an acronym for 'light detection and ranging.
Laser light pulses leave the LiDAR system, bounce off the ground or other objects, and return to the sensor. Distance is measured by tracking how long a pulse takes to return. Light moves incredibly fast and in all directions simultaneously. This means that LiDAR devices can create point clouds: complex scans made of millions of individual points.
Lidar point cloud Washington, DC [Source]. Point clouds are highly detailed 3D maps, illustrating everything from a downtown core to a national forest. Unlike radar and sonar, LiDAR is not necessarily inhibited by object interference.
This makes LiDAR particularly useful for mapping vegetated areas. For example, when surverying a national forest, the LiDAR emissions won't stop at the top of the tree canopy: they will make returns until hitting the ground. For DEMs, you would take a full LiDAR scan and then filter for the last return: remembering that the last return generally represents ground points.
With these filtered data points you can then create a bare earth map, one that excludes all but the surface of the Earth itself. For CHMs, the idea is similar. Filter for the first return in this case, the top of the tree and then subtract the final return the ground. This leaves the height of each tree in the area, allowing you to create a full canopy height map.
Luckily, there is a massive amount of open-source map data online. A few well-placed Google searches can unearth an abundance of valuable resources. Many counties maintain databases of their own GIS data, the majority of which is available for free download. There are also several open-source databases that are a great starting point for people looking to find a specific data type. NED offers a combination of both vector and raster data sets, most of which are available in three different size scales.
The downside of the crowdsource format is that nothing is vetted beforehand. Verifying data accuracy is difficult and some data sets are incomplete. That said, most anecdotal evidence points to a high degree of accuracy. With one of the more user-friendly search functions and the ability to download in bulk, USGS is an invaluable resource for cartographers in need of satellite or aerial data.
So despite the limitations, these data sets can be invaluable for people whose projects focus on those countries. This resource is unique because the data is climate and environment centered, making atmosphere, land, oceans, energy, and human life data more accessible.
GIS Introduction by David J. Buckey
There are several advantages and disadvantages for using either the vector or raster data model to store spatial data. These are summarized below. It is often difficult to compare or rate GIS software that use different data models. Some personal computer PC packages utilize vector structures for data input, editing, and display but convert to raster structures for any analysis. Other more comprehensive GIS offerings provide both integrated raster and vector analysis techniques. They allow users to select the data structure appropriate for the analysis requirements. Integrated raster and vector processing capabilities are most desirable and provide the greatest flexibility for data manipulation and analysis.
A data model is a way of defining and representing real world surfaces and characteristics in GIS. There are two primary types of spatial data models: Vector and Raster. Vector data is very common, and is often used to represent features like roads and boundaries. Vector data comes in the form of points and lines that are geometrically and mathematically associated. Types of Vector Data Points : One pair of coordinates defines the location of a point feature. A series of connected points - Actually, a set of series of connected points.
Geospatial Data Models
Data expands the richness of a map: giving the user a deeper, more insightful view of an area or project. Remember, as a concept, GIS can be defined as the intersection of data and location. In the last chapter, we covered the location component: mapping. However, GIS mapping requires more than coordinates. Vector data is, essentially, a list of coordinates: one that provides instructions on how an image should be rendered.
It only takes a minute to sign up. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets. Raster models are useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface. All I have understood from the above is that both vector and raster data constitute of "latitudes and longitudes", only.
Меган? - позвал он и постучал. Никто не ответил, и Беккер толкнул дверь. - Здесь есть кто-нибудь? - Он вошел. Похоже, никого. Пожав плечами, он подошел к раковине. Раковина была очень грязной, но вода оказалась холодной, и это было приятно. Плеснув водой в глаза, Беккер ощутил, как стягиваются поры.
Это тебе велел Фонтейн? - спросила. Бринкерхофф отвернулся. - Чед, уверяю тебя, в шифровалке творится что-то непонятное. Не знаю, почему Фонтейн прикидывается идиотом, но ТРАНСТЕКСТ в опасности. Там происходит что-то очень серьезное.
Беккер понимал, что через несколько секунд его застрелят или собьют, и смотрел вперед, пытаясь найти какую-нибудь лазейку, но шоссе с обеих сторон обрамляли крутые, покрытые гравием склоны. Прозвучал еще один выстрел. Он принял решение. Под визг покрышек, в снопе искр Беккер резко свернул вправо и съехал с дороги. Колеса мотоцикла подпрыгнули, ударившись о бетонное ограждение, так что он едва сумел сохранить равновесие. Из-под колес взметнулся гравий.
Да, но я на всякий случай заглянул в Интернет, запустив поиск по этим словам. Я не надеялся что-либо найти, но наткнулся на учетную запись абонента. - Он выдержал паузу. - Я, конечно, предположил, что это не та Северная Дакота, которую мы ищем, но на всякий случай проверил эту запись. Представь себе мое изумление, когда я обнаружил множество сообщений Энсея Танкадо.
Ты пробрался в мой кабинет. - Нет.
Джабба, - проворковала женщина в ответ. - Это Мидж. - Королева информации! - приветствовал ее толстяк. Он всегда питал слабость к Мидж Милкен.
Не волнуйся, приятель, ей это не удалось. У тебя скверный вкус на ювелирные побрякушки. - Ты уверен, что его никто не купил. - Да вы все спятили.
Ты сочтешь это сумасшествием, - сказал Беккер, - но мне кажется, что у тебя есть кое-что, что мне очень. - Да? - Меган внезапно насторожилась. Беккер достал из кармана бумажник. - Конечно, я буду счастлив тебе заплатить. - И он начал отсчитывать купюры.
Я сказал ему, что японец отдал свое кольцо - но не. Да я бы ничего и не взял у умирающего. О небо.