GIS Real Estate Suitability Example

Related pages: Elevation Data for Real Estate    Radon Gas Map

(Though variables in the suitability analysis example below are well-documented as affecting real estate location satisfaction, they are not meant to express the opinion of GIS Ag Maps. The purpose of the example is to describe a method of suitability analysis; specific characteristics of an analysis should be customized for an individual.)

In this example, factors for real estate suitability are: 1) being in a certain school district; 2) distance from a 100-year floodplain buffer; 3) distance from railways; 4) distance from major roadways; 4) elevation and topography. (Other variables worth considering are factories and chemical or power plants due to a variety of potential impacts.) More complex mathematical suitability analysis can also be developed.

1) Town boundary (extent of initial search)

2) School districts; never assume that the local school district boundary is the same as the town boundary (green and orange represent different school districts).

3) To this point, the suitable areas for real estate are within the local school district (green) and the town boundary, which is the area encompassed by the black line below.

4) 100-year floodplains (blue) should be considered for real estate suitability.

5) The 100-year floodplain extent can expand over time, so a buffer around the floodplain should be applied to increase the size to exclude some adjacent area. Below, the 100-year floodplain extent (darker blue) is shown with a 200 foot buffer (lighter blue) over an elevation map (darker shades of gray are lower elevation); the buffer corresponds to about 3 - 6 feet of additional elevation along the course of the floodplain. (The increased width from the buffer correlates to increased elevation that water needs to rise in order for a flood to occur.) To this point, the suitable area for real estate is within the black line away from the floodplain.

6) With all else being equal, for stationary objects, noise decreases 6 decibels (dB) as distance doubles. The About Noise page shows that this decrease is similar, but somewhat different, for a train because it is moving and is affecting by different surfaces and obstructions. For the purposes here we will use the 6dB per distance doubled amount. For example, if an object causes 50 dB of noise at 100 feet, it will cause 44 dB at 200 feet, and 38 dB of noise at 400 feet, and so on. Looking at data from the About Noise page, it can be seen that a train horn loudness is about 107 dB at 100 feet. An estimate of noise from other sources, such as vehicle noise, can also be found on the About Noise page.

Railways that affect extent of real estate search area are included below. Trains can impact real estate location suitability based on the noise from horns, engines, and rails.

7) The following graphic shows distances that are double from train rails. The white circles are intersections where trains sound the horn, while the white lines are where trains sound the horn along the track (1/4 mile before intersection; virtually through the entire town in this case). There buffers below are: 1) 200 feet (where the darker red meets the lighter red); 2) 400 feet (where the lighter red meets the darker orange); 3) 800 feet (where the darker orange meets the lighter orange); 4) 1,600 feet (where the lighter orange meets the yellow); 5) 3,200 feet (where the yellow meets the green); and 6) 6,400 feet (end of green). You can associate the loudness of a train at a distance with a familiar sound by viewing a noise estimation map (such as the map below) and looking at the chart the About Noise page and finding a sound you are familiar with that has a similar loudness. If you can find out how much noise your house keeps out (STC rating; mainly a function or walls, windows, and roof) you can estimate how loud outside noises will be inside a house.

For this example, suitable areas for real estate will be where the train noise has decrease by 30 dB (3,200 feet from the rail); as listed above, train horn noise is 107dB at 100 feet, so it would drop 6 dB at 200 feet, 12 dB at 400 feet, 18 dB at 800 feet, 24 dB at 1,600 feet, and 30 dB at 3,200 feet. A suitable area for this example then needs to be at the junction or where yellow meets green and beyond (away from the rail), keeping in mind that there are obstructions that affect noise per distance as well as soft (such as grass) versus hard surfaces.

8) To this point, the suitable areas for real estate are shown in light brown below , which are those areas that meet the criteria of being within the town boundary, local school district boundary, outside of the buffered floodplain, and at least 3,200 feet from the rail.

9) Highway and major routes through town (white lines) are also a noise source that can be lessened by distance, though there are many benefits to being closer to major roadways (so you may also want to be within a certain distance of a major roadway). Below are the highways and major routes through town.

10) For this example, we apply a noise buffer for major roadways, though (as previously stated), there are different benefits of being within a distance of a major roadway. Buffers can be created from major roadways similarly to how they were created from rail. There are six distances shown below to map the decrease of vehicle noise from highways and major routes through town. If you view the About Noise page you will find that at 50 feet, noise from these types of roadways produce 60 to 70 dBa. The buffers below are: 1) 100 feet (dark red meets red; and difficult to see at this scale); 2) 200 feet (where red meets orange); 3) 400 feet (where orange meets light orange); 4) 800 feet (where light orange meets yellow); 5) 1,600 feet (where yellow meets green); and 6) 3,200 feet (end of green). For this example, the 800 foot buffer will be deemed suitable, so the area where the light orange and yellow meet and beyond is suitable, so the decrease in noise is about 24 dB (but the amount is different in reality due to the fact vehicle are moving and surfaces and obstructions vary).

11) The areas with blue lines represents the same extent as in Step 8. It can be seen that there are suitable areas that include major roadway buffers beyond 800 feet (where light orange and yellow meet).

12) To this point, the suitable areas for real estate are those areas that meet the criteria of being within the town boundary, local school district boundary, outside of the buffered floodplain, at least 3,200 feet from the rail, and at least 800 feet from a major roads as described above (white area below; black lines are roads).

13) Elevation is shown below (darker shades are lower) along with streams and suitable areas to this point (within orange). Elevation can be used to base decisions on about suitable areas for real estate. For example, below you can see that the suitable areas lie in very different elevations.

14) Elevation data can be used to derive depression maps in GIS (within aqua) - depressions are areas that can collect water (depending on soil and other surface characteristics). It can be important to make sure that a location you are interested in is not located in a depression. In this example, there are no depression in the suitable areas so the search extent can stay the same, other than the area in the lower right.

Another elevation-based feature that can be used to make decisions about the location of real estate are basins divides. These are essentially ridgelines and are the highest local elevation; water is shed on either side of the divide (represented by red). You can see that there are basins divides that run across suitable areas; these areas tend to have overall drier surfaces as well as subsurfaces, and do not accumulate water. The floodplain and buffer areas are also shown below with suitable real estate areas.

After developing a suitability analysis, a real estate search can focus on specific areas suitable to you.  You can base suitable areas on any criteria you want, whether they are the same or different as those shown above (for example, you want want to be within a certain distance of major roadways).  Any type of data you know of that relates to real estate suitability can be mapped and applied in a manner right for you.