В отсутствие схемы расположения границу участка сравнивают с координатами смежного участка.

It is a formal set phrase meaning in the absence of or, more naturally in English, if there is no / when there is no.

So В отсутствие схемы расположения... means something like:

• In the absence of a layout/location plan...
• If there is no site plan...

This phrase is very common in official, legal, and technical Russian.

This is a chain of two nouns:

• схема = a scheme, plan, diagram
• расположение = location, placement, positioning

So схема расположения literally means a plan/diagram of the location/placement.

In context, it is a technical term, so a more natural English rendering might be layout plan, location plan, or site plan, depending on the field.

Схемы is genitive singular.

That happens because the phrase means absence of something. Russian expresses that something with the genitive:

• отсутствие чего? = absence of what?
• отсутствие схемы = absence of a plan

So in в отсутствие схемы расположения, the missing thing is схема расположения.

Because it depends on схема:

• схема чего?
• схема расположения = a plan of location/placement

So you get two linked genitives:

• отсутствие схемы
• схема расположения

This kind of noun stack is very common in formal Russian.

This contains two different relationships:

• границу is accusative singular because it is the direct object of сравнивают
• участка is genitive singular because it means boundary of the plot

So:

• границу = the boundary
• участка = of the plot

Together: the boundary of the plot.

This is a very common Russian construction called an indefinite-personal use.

Literally, сравнивают means they compare, but in sentences like this it often means:

• one compares
• people compare
• it is compared

In formal English, you would often translate it passively:

• the boundary is compared...

Russian often prefers this 3rd-person plural form in instructions, regulations, and technical descriptions when the doer is not important.

Because the verb pattern is:

• сравнивать что с чем = to compare something with something

So Russian uses:

• the first thing in the accusative
• the second thing with с
  • instrumental

Here that gives:

• границу = what is being compared
• с координатами = with the coordinates

This is a standard verb pattern you should memorize.

Смежный is a formal/technical word meaning adjacent, adjoining, or sharing a border.

So:

• смежный участок = an adjacent plot / adjoining parcel of land

This is especially common in land, cadastral, and legal language.

Both can be translated as neighboring or adjacent, but they are not identical.

• соседний = neighboring, nearby, next-door; more everyday and broader
• смежный = adjoining, contiguous, sharing a common boundary; more formal and precise

In land-registration or boundary contexts, смежный is usually the better word because it specifically suggests direct contact.

Russian often uses the present imperfective to describe:

• general rules
• standard procedures
• official instructions
• what is typically done

So сравнивают here does not mean are comparing right now. It means:

• they compare as a standard practice
• the boundary is compared

This is very normal in formal Russian.

It sets the condition first:

• If there is no layout plan, ...

That word order is very natural in formal Russian because it tells you the circumstances before the main action.

You could move it later, but the version with it at the front sounds more standard and clearer in official writing.

Because this is technical/legal style, where precision matters more than elegance.

The sentence refers to:

• the plot whose boundary is being checked
• the adjoining plot

Repeating участка avoids ambiguity. Russian official language often repeats nouns where everyday speech might use a pronoun.

Because they refer to different kinds of things:

• граница = the boundary, treated as one boundary line or one legal boundary
• координаты = coordinates, normally a set of points, so naturally plural

So the grammar reflects how the objects are conceptualized in technical language.

Not in a simple everyday sense. This is technical shorthand.

In cadastral or land-registration language, it means something like comparing the recorded or described boundary of one plot against the coordinate data of the adjoining plot.

So the wording is formal and compressed, not conversational. In ordinary speech, a speaker might explain the same idea more explicitly.