Geographic information pdf system

Where was a rock sample collected? Exactly where are all of a city's fire hydrants? If, for example, a rare plant is observed in three different places, GIS analysis might show that the plants are all on north-facing slopes that are above an elevation of 1, feet and that get more than ten inches of rain per year.

GIS maps can then display all locations in the area that have similar conditions, so researchers know where to look for more of the rare plants. By knowing the geographic location of farms using a specific fertilizer, GIS analysis of farm locations, stream locations, elevations, and rainfall will show which streams are likely to carry that fertilizer downstream. These are just a few examples of the many uses of GIS in earth sciences, biology, resource management, and many other fields.

We consider the product to be primarily an output of—rather than an input to—GIS. However, we recognize the demand for symbolized maps in GIS, and we are working on a companion product that will provide most US Topo To access the metadata file, download the GeoPDF file, open it in Acrobat Reader, click on the paperclip icon, then select a file from the list that appears a US Topo Map Symbols sheet is also included.

A CSV dump for The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way.

A flat map can show one or more--but never all--of the following: True directionsTrue distancesTrue The Bureau of Land Management and the U. Geological Survey have published a hub to enable easy visualization and access to geospatial data about Science Explorer.

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A short summary of this paper. A geographic information systems model for mapping risk of fasciolosis in cattle and buffaloes in Cambodia. Veterinary Parasitology — A geographic information systems model for mapping risk of fasciolosis in cattle and buffaloes in Cambodia S. Determinants were subjectively weighted according to their perceived relative importance before combining them to produce a risk-map of fasciolosis.

The estimates of risk reflect the actual prevalence of fasciolosis in most districts surveyed, suggesting that the epidemiological determinants and weightings used to produce the model were appropriate.

These results will be progressively refined as more detailed field surveys are completed to fully validate the model. All rights reserved. Introduction Tropical fasciolosis caused by infection with Fasciola gigantica occurs in most humid tropical regions of the world.

Cattle and buffaloes are the main hosts but other domestic animals and humans are also susceptible. E-mail address: marji uow. Tum et al. Nevertheless, control is not commonly practiced as most Cambodian farmers have minimal knowledge of fasciolosis. Furthermore, areas where the disease is most important, within which extension programs for control should logically be focused, have not been defined. Collection of prevalence data to enable such areas to be mapped would be costly and cumbersome.

However, maps showing gradations of risk of fasciolosis would serve the same purpose and can more easily be produced using GIS technology in conjunction with determinants of fasciolosis. GIS has been widely used for the surveillance and monitoring of vector-borne Mott et al. Yilma and Malone showed that GIS can be used to monitor the ecology of fasciolosis and to build a model to portray its complex rela- tionships.

Although the prevalence of fasciolosis is strongly correlated with the abundance of the snail intermediate host, the dynamics of fasciolosis in different regions are influenced by environmental variations and differences in number and management of animals, all of which can be modeled in GIS.

Spatial models have been developed using GIS to assist with control of fasciolosis in a range of locations from the temperate regions of Louisiana Malone et al. However, only four of these models were related to the control of F. Thus, the purpose of this study was to produce a map of Cambodia using GIS technology, which illustrates areas of high, medium, low, and negligible risk of fasciolosis in cattle and buffaloes as an aid to planners in the control of fasciolosis.

Materials and methods 2. The country covers an area of km2. The dominant features of the Cambodian landscape are lowlands and a large lake Tonle Sap , which occupy the center of the country, the delta of the Mekong River in the south, ranges of hills in the east, and mountain ranges in the southeast and north.

Determinants of fasciolosis in Cambodia A number of epidemiological studies have identified determinants of fasciolosis caused by F. Key geographic features of Cambodia. However, the actual risk of infection is influenced by the number and distribution of animals, especially cattle and buffaloes, the presence of infected snails, and grazing management which allows animals to access herbage or water containing metacercariae. Conceptual risk model A relatively simple mathematical model was developed to map the areas of potential risk of fasciolosis in Cambodia.

The model was constructed using GIS from individual data layers representing district boundaries, rivers, inundated areas, elevation, slope and agricultural land uses Table 1. For each environmental determinant chosen to build the potential risk model, values ranging from 0 to 3 were assigned to reflect the likelihood that fasciolosis would be transmitted. Each determinant was additionally weighted subjectively according to its perceived relative importance in contributing to a potential risk of fasciolosis Table 1.

For example, inundation was weighted by a factor of 3 because inundated areas are a favorable and usually a permanent habitat for the aquatic snails that are the intermediate host of F. However, the likelihood of infection varies within flooded areas. The greatest opportunities for infection of snails and livestock occur towards the end of the dry season, when residual water in inundated areas is lowest and cattle and buffaloes graze in these by then shallow areas rich in emergent vegetation.

Because of this, areas periodically inundated were assigned a value of 3. Land use categories considered to pose the highest risk and thus valued the highest were those that provided a favorable habitat for aquatic snails and were likely to be used as a grazing resource for cattle and buffaloes. Seasonally the margins of inundated areas are used for cultivation of rice recession rice as the water recedes.

Such use provides the opportunity for infection of snails in the rice fields with F. They then become a potential source of infection with metacercariae of animals that graze the stubble or rice stalks a common management practice , or drink residual water from the fields after harvest.

A similar risk is likely from irrigated rice fields where irrigation or sufficient rainfall enables growth of two or more annual rice crops, especially if dung from cattle or buffaloes is used as fertilizer. The likelihood of fasciolosis originating from single annual crop rain-fed rice fields, field crops and orchards, was considered to be lower as habitats of aquatic snails in such areas are usually restricted to the dams and channels that provide irrigation.

Access of animals to these habitats is also restricted to protect the sur- rounding crops, thus reducing the opportunity for infection of snails and, as a consequence, of animals that graze the margins or drink the water.

On the other hand, rain-fed rice fields those with only one crop annually usually have few snails as they die during the dry season and must recolonize each wet season from dry season refuges Suhardono and Copeman, The potential to acquire infection with F. The areas fringing major rivers were weighted by a factor of one as large rivers were considered to be less important habitat for snails than inundated areas and swamps. Within such fringing areas, however, stock with access to the riverbank are at greater risk of acquiring fasciolosis than those more remote and values were assigned accordingly.

Elevation and slope were also given weighting of one because they are less important determinants than land use or inundation. However, because the occurrence and suitability of aquatic habitats for snails decreases as elevation and slope increase, values were assigned to reflect this.

The GIS map data layer for each potential determinant, consisting of values ranging from 0 to 3 based on its perceived likelihood of facilitating infection with F. Maps so produced were multiplied together to produce a map of the overall potential risk. A map showing areas of actual risk was produced by multiplying the map of potential risk by the density map of cattle and buffaloes linked to district boundaries.

Faecal samples were collected opportunistically from cattle and buffaloes in 11 provinces. There were samples from the areas around Lake Tonle Sap, samples from the areas along the Mekong and Basac rivers, and samples from the areas far from either the rivers or the lake.

Faecal samples were analysed using a modified version of the Balivet egg count technique. Results and conclusions In this study only inundation, land usage, elevation, slope and distance from rivers were chosen to build a model of potential risk for fasciolosis Table 2. Although, rain- fall and temperature were shown to be important determinants for fasciolosis in Thailand and Ethiopia, they are unlikely to be important in Cambodia. Rainfall was excluded be- cause the annual flood that fills Lake Tonle Sap and inundates areas adjacent to major rivers originates primarily from melting snow in the upper reaches of the Mekong River rather than from local rainfall.

Moreover, following the peak of flooding, the common practice of cultivating irrigated rice recession rice at the periphery of flooded areas as the water recedes and the widespread use of draught cattle and buffaloes for preparation of these fields, provides a suitable aquatic habitat for the snails and an opportunity for their infection with F. Temperature was excluded from the model because, in Cambodia, it fluctuates little throughout the year and persists in the range favorable for snails.

The risk gradually declines with increasing distance from the major rivers and lake, and as elevation and slope increase. There is almost no risk of fasciolosis in the provinces that are located far from rivers and the lake, especially the upland areas. There are few suitable habitats for aquatic snails in these areas, and also fewer cattle and buffaloes, thus restricting opportunities for the necessary interaction between livestock and snails needed to promote fasciolosis.

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